2 HARDWARE AND SOFTWARE

2 Hardware and software

2.1 Mainframe computers and

supercomputers

Mainframe computers are often referred to simply as mainframes. They are

used mainly by large organisations for bulk data-processing applications such as

censuses, industry and consumer statistics, and

transaction processing. Most

individuals tend to use personal computers, laptops or tablets, but mainframes are

much larger and have more processing power than these and cost considerably

more to buy. In 2020, the cheapest mainframe would cost at least $75 000. In

the early days of computers, the central processing unit was very large compared

to modern-day computers and used to be housed in a steel cabinet. This was often

referred to as the ‘main frame’ and sometimes as the ‘big iron’. Although many

people thought that with the advent of PCs, mainframes would die out, they

have continued to evolve and are still in major use today, mainly because of their

features such as

RAS, which we will go into in more detail later in this section.

Most PCs and laptops used to have a single processor, but today they tend to

have a CPU with many cores which gives the effect of having many processors.

This allows these computers to carry out

parallel processing rather than the

serial processing of their predecessors. Serial processing is when the PC performs

tasks one at a time, whereas parallel processing allows several tasks to be carried

out simultaneously. Currently, the best performing PCs have a processor with

18 cores, which allows the computer to carry out 18 tasks at the same time,

resulting in much faster performance.

A mainframe computer can have hundreds of processor cores and can process

a large number of small tasks at the same time very quickly. A mainframe is a

multitasking, multi-user computer, meaning it is designed so that many different

people can work on many different problems, all at the same time. Mainframe

In this chapter you will learn:

+ thecharacteristicsandusesofmainframe

computers and supercomputers

+ thetypesandusesofsystemsoftware

+ theneedfor,typesandusesofutility

software

+ the use of custom-written software and off-

the-shelf software

+ thetypesandusesofuserinterfaces.

Before starting this chapter you should:

+ be familiar with the terms ‘application software’, ‘CPU’, ‘command

line interface’, ‘device’, ‘graphical user interface’, ‘medium’,

‘operating system’, ‘processor’ and ‘utilities’.

2.1 Mainframe computers and supercomputers

computers are now the size of a large cupboard, but between 1950 and 1990 a

mainframe was big enough to fill a large room, so you can see how much the

average mainframe has decreased in size while also improving its performance.

Mainframes are not the only computers within large companies as many

organisations own hundreds of personal computers (PCs) and laptops. Despite

their popularity amongst commercial organisations, most other people are

completely unaware of their existence. Mainframe computers have almost total

reliability, being very resistant to

viruses and Trojan horses.

Even more powerful are modern

supercomputers, which can have in excess

of 100 000 processing cores. In Chapter 1, batch processing of payroll was

described. A supercomputer can multiply different hourly wage rates from a

master file by a list of hours in a transaction file

for hundreds of workers in roughly the same

time that it would take a personal computer to

calculate the wages of just one employee. The Oak

Ridge National Laboratory in the USA launched

its

Summit supercomputer in 2018. It claimed, ‘if

every person on Earth completed one calculation

per second, it would take the world population

305 days to do what Summit can do in 1 second’.

The Summit supercomputer, however, fills a room

the size of two tennis courts.

2.1.1 Mainframe computers

The most advanced mainframe computer at the

time of publication was the IBM z15, shown in

Figure 2.1. The cabinet itself is taller than the

average person.

The IBM z15 with up to 190 cores and its

predecessor, the Z14 with 170 cores, are used

by large banking organisations, government

departments and large insurance organisations.

2.1.2 Supercomputers

V Figure 2.2 The Cray XC40 supercomputer

V Figure 2.1 The IBM z15

mainframe computer

2 HARDWARE AND SOFTWARE

This is a picture of the Cray XC40 supercomputer, which can have up to

172000 processor cores. Several countries have one of these and they use them

in the fields of weather forecasting and scientific research, such as the study of

astrophysics and mathematical and computational

modelling.

2.1.3 Characteristics of mainframe computers and

supercomputers

Longevity

Mainframe computers have great longevity, or lifespans. This is because they

can run continuously for very long periods of time and provide businesses with

security in the shape of extensive encryption in all aspects of their operation.

Governments, banking organisations and telecommunications companies still

base their business dealings on mainframes. Many of these computer systems

have existed for decades and are still working well. To shut them down then

dispose of the hardware is very expensive, as is the hiring of companies to

securely remove their data.

Although they tend not to cause problems, there are several factors threatening

their continued existence. One is the lack of experienced IT professionals who

can maintain or program mainframes. Many of the older computer systems still

work on the COBOL programming language, which is being taught at fewer and

fewer universities in recent times. It has been gradually replaced by courses in

Java, C and Python. Yet as recently as 2017, the news agency Reuters stated that

95 per cent of ATM transactions were carried out by computers using COBOL

code. Another threat to mainframes comes from new technological developments,

specifically Cloud computing, which is accessible from anywhere, thereby

reducing the need to maintain expensive hardware within an organisation. The

solution may well be to combine the use of mainframes with Cloud computing,

thus giving organisations the flexibility and accessibility of the Cloud, while at the

same time providing the processing power and security of the mainframe.

Despite these threats, the mainframe has remained popular for a long time,

largely as a result of its efficiency and dependability. The mainframe is still

able to process more transactions and calculations in a set period of time when

compared with alternatives and it continues to operate with a minimum of

downtime, which means that companies can operate 24 hours a day, every day.

In contrast, supercomputers have a lifespan of about five years. Research

institutions and meteorology organisations are always looking for faster ways to

process their data and so, unlike companies using mainframes, will tend to look

at replacing their existing systems whenever much faster supercomputers come

on to the market. Companies using mainframes are more inclined to modernise

them using different software tools.

RAS

The term ‘RAS’ is frequently used when referring to mainframe computers and

stands for reliability, availability and serviceability. RAS is not a term that is

used, on the whole, with supercomputers.

Reliability

Mainframes are the most reliable computers because their processors are able

to check themselves for errors and are able to recover without any undue effects

on the mainframe’s operation. The system’s software is also very reliable, as it is

thoroughly tested and updates are made quickly to overcome any errors.

2.1 Mainframe computers and supercomputers

Availability

This refers to the fact that a mainframe is available at all times and for extended

periods.

Mean time between failures (MTBF) is a common measure of

systems, not just those involving computers. It is the average period of time that

exists between failures (or downtimes) of a system during its normal operation.

Mainframes give months or even years of system availability between system

downtimes. In addition to that, even if the mainframe becomes unavailable

due to failure, the length of time it is unavailable is very short. It is possible

for a mainframe to recover quickly, even if one of its components fails, by

automatically replacing failed components with spares. Spare CPUs are often

included in mainframes so that when errors are found with one, the mainframe

is programmed to switch to the other automatically. The operator is then alerted

and the faulty CPU is replaced, but all the time the system continues to work.

Serviceability

This is the ability of a mainframe to discover why a failure occurred and means

that hardware and software components can be replaced without having too

great an effect on the mainframe’s operations.

Security

In addition to their other characteristics, mainframes have greater security

than other types of computer systems. Data security is considered to be the

protection of data from intentional or accidental destruction, modification or

disclosure. As has already been mentioned, mainframes are used to handle large

volumes of data. Most of this is personal data and, especially in the banking

sector, it has to be shared by the banks with customers. This means that the

data has to be extremely secure so that only those users entitled to see the data

can do so; in other words, customers must be able to see their own data but not

each other’s. This applies to other uses of mainframes. Many companies store

the personal information of their employees, customers, and so on. Fortunately,

the mainframe computer has wide-ranging security that enables it to share a

company’s data among several users but still be in a position to protect it. A

mainframe has many layers of security including:

» user identification and authentication, although more and more systems are

using multi-factor authentication, which is a combination of two or more of

the following: a password, a physical token, a biometric identifier or a time-

restricted randomised PIN

» levels of access, which means that it depends on a user’s level of security as

to which sets of data they can access

» encryption of transmitted data and data within the system

» secure operating systems

» continual monitoring by the system for unauthorised access attempts.

In addition to the use of supercomputers to perform massive calculations, they

may also be used to store sensitive data such as DNA profiles. This obviously

requires a very high level of security. Most supercomputers use end-to-end

encryption, which means that only the sender or recipient is able to decrypt and

understand the data.

Performance metrics

The performance metrics of a computer are basically the measures used to

determine how well, or how fast, the processor deals with data. The speed of a

mainframe’s CPU is measured in millions of instructions per second (

MIPS).

2 HARDWARE AND SOFTWARE

However, it is not always the best measure, because not all instructions are the

same. Mainframes use a very large number of different instructions, with some

being straightforward and easy to carry out, while others can be more complex

and slower to process. An application using five million simple instructions will

take a lot less time than one using five million complex ones. In addition, the

number of available instructions is increasing as time goes by and mainframes

improve. It is important that the comparison between the performance of one

mainframe and another is made by measuring how fast the CPUs are when

carrying out the same task. This is referred to as a benchmark test. This measure

is usually obtained when processing application software. MIPS are often linked

to cost by calculating how much a mainframe costs per one million instructions

per second.

Supercomputers use a different set of metrics. As they are used mainly with

scientific calculations, their performance is measured by how many FLoating

point Operations can be carried out Per Second (

FLOPS). Since the original

supercomputers were developed, speeds have increased incredibly and are

now measured in petaflops. One petaflop is 1 000000000 000 floating point

operations per second. Experts are already using the term exaflops, which are

1000 times faster than petaflops, and are expecting the first supercomputer

to attain this speed sometime in the current decade. The speed of the current

fastest supercomputer, at the time of publication, is 148 petaflops and even the

tenth fastest operates at 18 petaflops.

Volume of input, output and throughput

The volume of input, output and throughput has to be considered when

describing computers.

Mainframes have specialised hardware, called peripheral processors, that deal

specifically with all input and output operations, leaving the CPU to concentrate

on the processing of data. This enables mainframes to deal with very large

amounts of data being input (terabytes or more), records being accessed, and

subsequently very large volumes of output being produced. Modern mainframes

can carry out many billions of transactions every day. This large number of

simultaneous transactions and extremely large volumes of input and output in a

given period of time is referred to as ‘throughput’.

A supercomputer is designed for maximum processing power and speed, whereas

throughput is a distinct mainframe characteristic.

Fault tolerance

A computer with fault tolerance means that it can continue to operate even if

one or more of its components has failed. It may have to operate at a reduced

level, but does not fail completely. Mainframe computers have the characteristic

of being fault-tolerant in terms of their hardware. While in operation, if a

processor fails to function, the system is able to switch to another processor

without disrupting the processing of data. The system is also able to deal with

software problems by having two different versions of the software. If the first

version produces errors, the other version is automatically run.

Supercomputers have far more components than a mainframe, with up to a

thousand times more processors alone. This means that statistically, a failure

is more likely to occur and consequently interrupt the operation of the system.

The approaches to fault tolerance are much the same as those for mainframe

computers, but with millions of components, the system can go down at any

time, even though it tends to be up and running again quite quickly.

2.1 Mainframe computers and supercomputers

Operating system

Most mainframes run more than one operating system (OS) at any given time

and the use of z/OS, z/VM

, and Linux

(which are all different operating

systems) at the same time often occurs. The OS on a mainframe divides a

task into various sub-tasks, assigning each one to a different processor core.

When each sub-task has been processed, the results are recombined to provide

meaningful output. This is called parallel processing and it is what makes a

mainframe far more efficient than a PC, which, despite having more than one

core these days, has a very limited capability regarding parallel processing.

Supercomputers tend to have just one OS, Linux, but most supercomputers

utilise

massively parallel processing in that they have many processor cores,

each one with its own OS. Linux is the most popular, mainly because it is open-

source software, that is, it is free to use.

Type of processor

Early mainframes had just one processor (the CPU), but as they evolved

more and more processors were included in the mainframe system and the

distinction between the terms ‘CPU’ and ‘processor’ became confused. One

major mainframe manufacturer called them ‘CPU complexes’, which contained

many processors. The number of processor cores found in a mainframe is now

measured in the hundreds.

By contrast, supercomputers have hundreds of thousands of processor cores.

Unlike mainframes, modern supercomputers use more than one

GPU or

graphics processing unit.

Heat maintenance

Because of the large number of processors in both mainframes and

supercomputers, overheating becomes a major problem and heat maintenance

or heat management, as it is often called, has to be implemented. In the early

days of mainframe computing, the heat produced by the computer could not

be controlled using cooling by fans. Liquid-cooling systems had to be used.

When integrated circuits were developed in the 1970s and became universal in

the 1980s, mainframes were developed which produced less heat and so fans

were able to dissipate the heat. However, recent developments in mainframe

technology involving more powerful hardware mean the overheating issue has

resurfaced. More powerful systems produce more heat. What were considered to

be a relatively cheap option – air cooling systems – are becoming more complex

and more expensive to use in more powerful systems. At the same time, water-

cooling solutions have become more cost-effective. We now appear to have come

full circle and mainframe manufacturers are once again recommending water-

cooled systems for larger machines.

The overheating problem has always been present with the use of

supercomputers. The large amount of heat produced by a system also has

an effect on the lifetime of components other than the processors. Some

supercomputers draw four or more megawatts of power to keep them operating

at high efficiency. That is enough to power several thousand homes! This,

together with having so many processors very close together, results in a great

deal of heat being produced and requires the use of direct liquid cooling to

remove any excessheat.

2 HARDWARE AND SOFTWARE

Activity 2a

Explain what is meant by these terms:

1 MIPS

2 FLOPS

3 Fault tolerance

2.1.4 Mainframe computer uses

Mainframe computers play a vital role in the daily operations of many

organisations. Finance companies, health care providers, insurance companies,

energy providers, travel agencies, and airlines all make use of mainframes.

By far and away, however, the greatest use of mainframes is in the banking

sector, with banks throughout the world using mainframes to process billions

of transactions. The key benefit of mainframes is their ability to process many

terabytes of data, which is very useful when carrying out batch processing.

Batches of transactions are processed by the mainframe without user

interaction. Large volumes of data are read and processed, then customers’

bank statements, for example, are output. During batch processing, which

usually takes place overnight, other jobs can be carried out such as back-ups.

Mainframes are also used in other areas suchas censuses, industry statistics,

consumer statistics, and transaction processing.

Census

Census is a term that, when used alone, normally refers to a population census. A

population census is an official survey of the people and households in a country

that is carried out in order to find out how many people live there. It is used

to obtain details of such things as people’s ages and types of employment. The

amount of data that has to be processed is enormous. The processing of census

data has long been associated with computers. The

UNIVAC 1, which was the

first computer on general sale to organisations or businesses, was purchased

by the United States Bureau of the Census in 1951. After that, technological

innovations have seen the production of different generations of mainframes and

other developments have enabled census agencies to become more knowledgeable

in the way they process and manipulate data. A census usually takes place every

ten years. Not surprisingly, as populations increased, each census produced more

data and so the use of mainframes to process the data was crucial. However, by

the year 2000, the increase in processing power and storage capacities of PCs

provided many countries with the opportunity to take a new approach and many

are deciding against buying expensive mainframe computers.

Industry statistics

Industry statistics are statistics that are recorded regarding trends in different

industries, such as those that process raw materials, make goods in factories,

or provide services. They can include the number and names of businesses,

the number of employees and wages paid. Some businesses in certain sectors

of industry need mainframes to process the vast amount of data which helps

to identify their major competitors. It shows their competitors’ share of the

market and the trends in their sales. This helps to identify those products

which could compete profitably with other businesses. Where companies do

not feel the need to process their own data, they can obtain reports from

organisations that collect the data for them and those companies could use

mainframes for this purpose.

2.1 Mainframe computers and supercomputers

Consumer statistics

Consumer statistics allow businesses to assess the demand for their product, that

is how many people need or want that type of product. They can inform them

about the range of household incomes and employment status of those consumers

who might be interested in the product so that a price can be set. This data will

also inform businesses of where the consumers live for local sales or how inclined

they are to use the internet for shopping. It may also allow businesses to know

how many similar products are already available to consumers and what price

they pay for them. These statistics produce an incredible amount of data and the

organisations that produce these statistics are likely to use mainframes.

Transaction processing

Transaction processing can consist of more than one computer-processing

operations, but these operations must combine to make a single transaction. Each

of the operations that constitute the transaction must be carried out without errors

occurring, otherwise the transaction will be deemed to have failed. A transaction-

processing system, in the event of an error, will remove all traces of the operations

and the system will continue as though the transaction never happened. However,

if there are no errors, the transaction is completed and the relevant database is

updated before the system continues on to the next transaction. All this, of course,

has to happen in milliseconds, as it must seem to the user that their transaction has

been carried out immediately. Transaction processing involves the use of online

processing, which was looked at in Chapter1.

One example of transaction processing is the transfer of a sum of money

from one bank account to another, for example when you pay for goods at a

supermarket checkout. The bill might be $100. The customer needs to transfer

$100 from their bank account to the supermarket’s bank account. To make it

simpler, consider that the customer and the supermarket use the same bank.

There are two operations involved, one is that $100 must be subtracted from

the customer’s account balance and the other is that $100 must be added to

the supermarket’s account balance. If either of these operations fails then the

transaction will be cancelled by the mainframe, or the bank would not be able

to balance the books at the end of the day.

Why is the mainframe computer so well suited to transaction processing? First, the

effectiveness of a transaction-processing system is often measured by the number

of transactions it can process in a given period of time. We know a mainframe can

perform hundreds of MIPS. The system must be continuously available during

the times when users are entering transactions and the system must be able to deal

with hardware or software problems without affecting the integrity of the data. It

must also be possible to add, replace, or update hardware and software components

without shutting down the system. With its ability to transfer processing from one

core to another, the mainframe is more than suitable for thetask.

Activity 2b

Give two reasons why the use of mainframes for carrying out censuses is reducing.

2.1.5 Supercomputer uses

The first use of supercomputers was in national defence, for example, designing

nuclear weapons and data encryption. Supercomputers have become important

in the field of scientific research, particularly quantum mechanics. They have

also become essential for weather forecasting. There are now many other uses of

2 HARDWARE AND SOFTWARE

supercomputers, one of which is drug research. Before a drug is tested, it needs

to be developed, but it does not start with a blank sheet of paper. Quite often the

results of previous research are stored and then compared with the results of the

new drug that is being developed. The computer is used to monitor the amount

of ingredients that are being used. It is important that the researchers can change

these amounts by the smallest fractions. Modern drug research involves the use of

complex computer

models to see how changing the structure of the drug affects

the way the body reacts. Computer models can also help to predict any side effects.

As the changes to the model are so tiny and the number of times the model must

run is so high, a computer with great computational power is required. This makes

the use of supercomputers indispensable to drug manufacturers.

Another field where supercomputers are used is genetic analysis. Finding the

genes that make humans susceptible to disease has always been very difficult.

There are so many genes, and variations of them, that humans were unable to

carry out the calculations required to identify those genes responsible. With

the advent of supercomputers, however, this task has become more manageable,

reducing the time taken to perform the calculations from months to minutes.

Here, we will focus on three uses of supercomputers: quantum mechanics,

weather forecasting and climate research.

Quantum mechanics

Quantum mechanics is the study of the behaviour of matter and light on the

atomic and subatomic scale. It attempts to describe the properties of the constituent

parts of an atom, such as electrons, protons and neutrons, and how they interact

with each other. They do not behave in the same way as larger bodies, which

obey the laws of physics. You do not need to understand quantum mechanics,

but it is important to realise that there are a very large number of calculations

which require great accuracy and thus require the use of a supercomputer. The

Juqueen supercomputer in Germany, now decommissioned, was used by a team

of physicists to calculate the difference in mass between a neutron and a proton

as well as predicting the make-up of dark matter. The Juqueen had a maximum

performance of 5 petaflops with 459 000 cores. It hasbeen replaced by the Juwels

supercomputer with a performance of 12 petaflops (although the developers are

currently working to increase that to 70 petaflops!).

Weather forecasting

Weather forecasting is based on the use of very complex computer models.

Data from the sensors at weather stations around the world is input to the

model and then many calculations are performed. Records of previous weather

conditions have also been collected over a very long period. Using the past

weather readings, the computer examines similar patterns of weather to those

being experienced at the moment and is able to predict the resulting weather.

Variables such as atmospheric pressure, humidity, rainfall, temperature, wind

speed and wind direction are recorded using computerised weather stations

around the world. These readings, together with observations from radar,

satellites, soundings from space, and information from ships and aircraft, help

the supercomputer to produce a 3-D model of the Earth’s atmosphere. Because

of the complexity of the calculations, and the very large number of them that

need to be carried out, they can only run effectively on supercomputers.

In 2017, the UK Meteorological Office commissioned three Cray XC40

supercomputers to help with formulating its weather forecasts. Together they

are capable of running at 14 petaflops and have a total of 460 000 cores, each of

which is slightly faster than those found in a quad (4) core laptop!

2.1 Mainframe computers and supercomputers

Climate research

This is an extension of the use of IT in weather monitoring. Climate is

measured over a much longer timescale. The data collected over several decades

can be used to show the trends of different variables over time. For example,

the levels of nitrogen dioxide, sulphur dioxide and ozone are monitored to

determine air quality. Rivers are monitored, measuring different variables such

as temperature, pH, dissolved oxygen, turbidity (the cloudiness of the water

caused by minute particles being present), and water level.

Climate is now being looked at from a global point of view. The planet Earth

can be regarded as a complex system which has many different constituent

parts, such as heat from the Sun, ocean currents, vegetation, land ice as found

in Greenland and the Antarctic, sea ice as found in the Arctic, weather and

climate, volcanoes and, of course, humans. The interactions of each of these

components within the Earth system can be described in mathematical terms.

However, just as with weather forecasting, there are very many variables which

have to be collected and complex calculations which need to be carried out. We

have to rely on computer models to help us understand how the system works.

Climate is one component of this planet’s system and only supercomputers are

able to run the models that represent the interactions between the components

of this system. CESM

, the Community Earth System Model, is the most

widely used climate model in the world today. It includes modules which allow

for atmosphere, land, ocean, sea ice and land ice, and uses various equations to

mimic the process of climate change using a virtual environment created on the

supercomputer.

Many people and organisations are becoming involved in developing supercomputer

climate models as climate change is developing into a potentially catastrophic

situation. In 2019, a team of students from the Sun Yat-sen University in Guangzhou,

China, won the e-Prize at the 2019 ASC Student Supercomputer Challenge (ASC19)

finals. They reduced the full-mode operation time of CESM to 1.83 hours.

Activity 2c

Give two reasons why supercomputers are used in weather forecasting.

2.1.6 Advantages and disadvantages of mainframes and

supercomputers

Advantages of mainframe computers

Mainframes are very reliable and rarely have any system downtime. This is one

reason why organisations such as banks use them. Most other systems do fail

at some point and then have to be rebooted or restarted, as most people who

use laptops or PCs will know. In addition, hardware and software upgrades can

occur while the mainframe system is still up and running.

Mainframes are getting faster and more powerful every year and are completely

outperforming PCs, laptops and other devices.

Mainframes can deal with the huge amounts of data that some organisations

need to store and process. Most organisations that use mainframes would

find it exceptionally difficult to transfer all the data they have stored on their

current mainframe to an alternative system. Because of a mainframe’s ability

to run different operating systems, it can cope with data coming in a variety of

database formats which other platforms would find problematic.

2 HARDWARE AND SOFTWARE

Mainframes have stronger security than other systems with have complex

encryption systems and authorisation procedures in place.

Disadvantages of mainframe computers

Mainframes are very expensive to buy and can only be afforded by large

organisations such as multinational banks. There is also a high cost for the

personnel required to run and maintain them. Large rooms are required to house

the system, which is not needed with other systems. As mainframes become more

advanced, the cooling systems needed become more expensive to install and run.

Many organisations are migrating to Cloud-based services so they do not have

to buy their own system or hire the expertise required. The software required to

run mainframe systems is more expensive to buy than using the Cloud.

Advantages and disadvantages of supercomputers

Supercomputers are the fastest data processing computers but are also the

most expensive to buy and install. The Summit supercomputer, which at the

beginning of 2020 was the world’s fastest supercomputer, cost $200 million to

build compared with IBM’s latest mainframe which costs between $250 000

and $4 million depending on the organisation’s requirements.

Most supercomputers have one operating system, whereas mainframes can have more

than one. Supercomputers are less fault tolerant than mainframes meaning they are

less likely to recover as quickly in the event of the failure of one component, and are

down more often than mainframes, although not as often as some other systems.

Supercomputers use massively parallel processing, which makes them more powerful

compared to the parallel processing of mainframes, and much more powerful than

PCs which have far fewer processor cores than mainframes or supercomputers.

2.2 System software

System software refers to the programs that run and control a computer’s

hardware and application software. Examples of system software are compilers,

interpreters, linkers, device drivers, operating systems and utilities.

2.2.1 Compilers

Most software that runs on computers is in machine code, which is stored in

binary form within the computer. Machine code consists of the instructions

that computers understand and each instruction is actually a number written in

binary. Unfortunately, programmers who write the software for computer users

find it difficult to use machine code for programming purposes. In the early

days of computing it was felt necessary to develop languages which programmers

could understand and was close to their use of everyday language.

Some of the early high-level languages developed included:

» FORTRAN (Formula Translation) was the first high-level language to be

developed. It was very technical and mathematical in nature. FORTR AN is

rarely used these days, but still remains popular for simulating large physical

systems, such as the modelling of stars and galaxies. The fact that it is still

widely used by physicists today often mystifies computer scientists, who

regard it as being out of date.

» COBOL (Common Business-Oriented Language) was developed not

long after FORTRAN to help businesses. Unlike FORTR AN, which relied

2.2 System software

on mathematical equations, COBOL tended to use simple expressions, such

as SUBTRACT money FROM account GIVING balance, rather than an

equation like bal=acc-mon.

» LISP (List Processor) was also an early high-level language. In LISP, simple

statements often start with the mathematical operator, such as (+ 2 4) which

would calculate 2+4. LISP was used extensively in the early years of AI but,

apart from its use in association with CAD, it is rarely used today.

Most high-level language programming for modern-day systems is done using

languages such as C++, C#, Visual Basics or Pascal, among others. These

have largely replaced the other languages mentioned above. However, the

development of all these high-level languages led to the need for software which

could translate a program written in high-level language into the machine code

that computers could understand.

A compiler is software (a program) that processes statements written in a high-

level programming language and converts them into machine language or code

that a computer’s processor understands and can execute. In other words, it

translates a high-level language program called source code into an executable

file called object code. The compiled program is then run directly without the

need for the compiler to be present.

Although compilers translate the whole program as one unit, they often need to

make more than one pass through the program to do this. This is because after

translating, it may become apparent that line 10 of the program refers to a statement

at line 5. The first pass picks up this type of information and then the second pass

completes the translation. The whole program is still effectively translated in one go

before it is executed. However, some programming languages, such as Pascal, have

been designed so that they would only require one pass. The object code is machine

code that the processor can execute one instruction at a time. A compiler produces a

list of error messages after it has translated the program. These cannot be corrected

without going back to the source code.

2.2.2 Interpreters

An interpreter translates the high-level language program one statement, or

line, at a time into an intermediate form, which it then executes. It continues

translating the program until the first error is met, at which point it stops. This

means that errors are located by the programmer, exactly where they occur. An

interpreter has to do this conversion every time a statement is executed.

An interpreted program can be transferred between computers with different

operating systems because it remains in the form of source code, but it needs to

be translated in each computer it is moved to. This takes more time than with

a compiler, but it means that the program can be distributed regardless of the

processor or operating system (OS) of the computer. The computer that it is

transferred to must have a suitable interpreter however; if the interpreter needs to be

supplied together with the program, the overall process is more complicated than

with a compiler. Unlike with a compiler, translation occurs at the same time as the

program is being executed. The interpreter has to be resident in memory in order

for the program to be executed. Interpreters just run through a program line by line

and execute each command. As a result, another benefit of using an interpreter is

that only a few lines of the program need to be in memory at any one time, saving

memory space.

There are other benefits of using interpreters, such as they help programmers

when they are developing programs. Interpreters are able to execute each

2 HARDWARE AND SOFTWARE

statement as it is entered and are able to generate helpful error reports. This

means that interpreters can be used during program development allowing a

programmer to add a few lines at a time and test them quickly.

Some high-level language programs such as Python

can be translated using a

combination of a compiler and an interpreter. It is possible for the program to

be translated or compiled into what is called ‘bytecode’. This is then processed

by a program called a ‘virtual machine’, which is often an interpreter, instead of

by the processor within the computer.

Activity 2d

Describe the purpose of compilers and interpreters.

2.2.3 Advantages and disadvantages of interpreters

compared with compilers

Advantages of interpreters Disadvantages of interpreters

While a program is being compiled, if it is a major

application and takes a long time, the programmer has to

wait, doing nothing, before they can correct any errors.

With an interpreted program the programmer can correct

errors as they are found.

The execution process is slower for an interpreted program

as each statement must be translated before execution,

whereas once a program has been compiled it executes

all in one go. The time it takes to compile a program can

be long but once it is compiled it does not have to be

translated, which compares favourably with an interpreted

program which has to be translated every time it runs.

Debugging is easier with an interpreter as error messages

are output as soon as an error in a statement is

encountered, which gives the programmer the opportunity

to correct the error there and then. With a compiler all the

error messages are output at the end of the process and

errors can be difficult to locate and correct.

With an interpreted program, the source code must

always be available, which can lead to software copyright

infringement or intellectual property rights being at

risk. With a compiled program, the source code has been

translated and machine code is difficult to understand and

alter.

A compiled program will only run on a computer with the

same operating system as the computer it was originally

compiled on, whereas an interpreted program will still

be in its original source code and so it will work on any

system with the appropriate interpreter.

Compiling a program uses more memory than interpreting

it as the whole program must be loaded before translation,

whereas with an interpreter only a few statements of the

program have to be in memory at any given time. This

means that small pieces of code can be tested to make sure

they work before continuing with the rest of the program.

V Table 2.1 Advantages and disadvantages of interpreters compared with compilers

There may be times when programmers wish to transfer their program to another

computer which has a different operating system and processor. In this case they

tend to write their programs in high level languages which use interpreters.

For compiled languages, it is possible to use a cross compiler, although this

can be complicated. The computer the program is written on is called the host

computer. The computer which the program is to be run on, after compilation,

is called the target computer. One problem with using a cross compiler is that

the compiled program will then no longer run on the host computer.

2.2 System software

Another problem comes as a result of a cross compiler tending to be a slimmed-

down version of a ‘native’ compiler (the compiler normally found on the host

computer so that the compiled program can be run on that computer). The

cross compiler produces more errors and mistakes than a native compiler. In

addition, the compiled code can run slower on the target machine than if it had

been produced on that machine.

2.2.4 Linkers

A linker, or to give it its full name a link editor, is a system program that combines

object files or modules that have been created using a compiler, into one single

executable file. Most programs are written in modular form. That is to say, a

number of programmers, write separate pieces of code, or modules that form the

required program when combined, which has the advantage of saving time than if

one person wrote the whole code although it is still possible for one person to write

all the modules. If there is an error only that module hasto be corrected.

In short, a linker is used to combine different modules of object code into one

single executable code program. It could be that a large program can only be

compiled in small parts because there may not be enough RAM to hold the

whole program and the compiler program. The parts of the program can be

stored on backing storage and then, one at a time, each part is brought into

RAM and compiled. The resulting object code is then saved to the backing

storage. When all the parts have been compiled, the compiler is no longer

required to be in RAM, all the pieces of object code can be brought back into

RAM and the linker can be used to combine them into the complete program.

An advantage of using linkers, therefore, is that programs can be written in

modules which requires less RAM so saving money. The disadvantages are

that there can be problems with variable names (this term will be explained in

Chapter 4) and also documentation has to be more detailed and takes longer to

write, or read when completed.

2.2.5 Device drivers

A device driver is a small program that enables the operating system (OS) and

application software to communicate with a hardware device. One example is

a printer driver which acts as an interface between the OS (or any application

software that is running) and the printer. The user, through the application,

might want to print information. The application tells the printer driver and the

printer driver tells the printer. This, in effect, allows the user to have control of

the device. Other devices which need drivers are sound cards, monitors, mice,

SSDs, network cards, keyboards, disk drives and many other items of hardware.

The software used by a computer tends to be created by different companies to

those that manufacture hardware. This results in software which uses a different

type of language to the hardware. There has to be some means of converting

the languages so that the software is able to communicate with the hardware

and vice versa. Think of a Spanish person who knows no French trying to

communicate with a French person who speaks no Spanish. They would not be

able to understand each other. If, however, they managed to find some translating

software, that is a program that could convert Spanish to French and French to

Spanish, they could run that software on a computer and be able to communicate.

The device driver, which is, after all, a piece of system software, performs the same

function as translating software. So, application software such as a word processor

sends information to a driver saying what it wants the hardware to do; the device

driver understands this and then tells the hardware what it needs to do.

2 HARDWARE AND SOFTWARE

If the appropriate driver is not installed, the computer is unable to send to or

receive data from the hardware devices. This means, in effect, the device will

not work. Modern operating systems are supplied with many drivers that allow

hardware to work at a basic level. However, if the OS of a computer does not

recognise certain features of the device, it will not work without drivers. It is

possible to connect any keyboard or mouse into a computer and it may work.

However, if that keyboard has any special keys or features or the mouse has extra

buttons, they will not work until the drivers are installed. In addition, drivers

that are produced for a specific OS will rarely work with an alternative OS.

2.2.6 Operating systems

Before an operating system (OS) is loaded the computer has to boot up. Booting

up a computer is starting it up by loading the BIOS. BIOS is stored in ROM

and is the Basic Input/Output System for the computer which executes during

boot-up. It checks various devices are present. It then loads the OS.

An OS is system software that manages computer hardware and software

resources as well as interacting with device drivers. Some of the device drivers

are separate to the OS, but are often included by the provider of the OS. The

OS acts an interface between the user and the computer, as well as supplying

important utilities for managing the computer. A utility program is a type of

system software that assists users in controlling or maintaining the operation of a

computer, its devices or its software. The OS also acts as an interface between an

application program and the computer hardware, so that an application program

can communicate with the hardware. To sum up, an operating system interacts

with application software, device drivers and hardware to manage a computer’s

resources, such as the processor, RAM, storage space, and peripherals.

For nearly all types of computer, the operating system program is large and

would occupy too much ROM, so most of it is stored on a hard disk. However,

the instructions for loading the operating system are stored in ROM and are

executed every time the computer is switched on.

One of the major functions of an operating system is to manage the computer’s

memory. The OS allocates a particular part of RAM for each program, whether it

is an application, system software or a utility that is running. It needs to make sure

that instructions and data from one program do not spread into another program’s

memory allocation, otherwise data can get corrupted and the computer could crash.

Another of the main functions of an OS is to manage data input and output. To

do this, it needs to be able to respond to input devices in order to receive and

manage that data. It does this by communicating with the device driver so that

it can receive data from the input device. It also uses device drivers when it sends

data or instructions to the printer.

The OS manages the storing of files on, as well as the loading of them from,

backing storage. It knows the names of each file and exactly where they are stored

on the hard disk, tape, pen drive or SSD. It also keeps a record of any empty

spaces on the medium so that it knows where new files can be stored. Using a

disk drive as an example, it requests from the disk drive the position of the first

available free storage location on the disk. It then records on the disk theposition

of the start of file and the end of file, as well as other details of thefile.

Strictly speaking, multitasking and multi-programming systems are not the

same thing. However, the OS has the same responsibility in both, in that it must

allocate time to each task or program fairly, so that all tasks or programs get a

reasonable amount of time. Most computers these days are able to multitask,

2.3 Utility software

so we will concentrate on those here. The OS loads the software in RAM for

each task and the computer gives each application a tiny amount of time before

moving to the next task. This process is repeated for however many tasks or

programs are running at the same time.

Another responsibility of the OS is to display error messages to the user should

an error occur which requires the user to intervene. A typical error might be

that a user, when they are trying to save their work, types in a symbol that is not

allowed in the file name, such as /. The OS will output a message saying that it

is an invalid file name and will not resume until the user takes action.

When a user logs in to a system, it is the OS that deals with this. Passwords are

no longer stored as plaintext, but are encrypted. A calculation is performed on

the password and the result is stored. When a password is entered by a user,

the calculation is performed again by the OS. If the result is the same as the

previous calculation result stored for that user, then the OS allows the user to

access the system. Even when a user has successfully logged in to a system, they

may still only have permission to access certain files. These are often referred to

as file permissions or access rights. Some of the files may be particularly sensitive

and only certain people will be allowed to look at them. In general, it is the

operating system’s responsibility to handle the security of the system.

When a user wishes to shut down the computer, the OS has to safely close all

software running on the computer. It then shuts itself down bit by bit before

finally sending a signal to the power management hardware to turn off the power.

Activity 2e

List the different functions of an operating system.

2.3 Utility software

2.3.1Theneedforutilitysoftware

Utility software is a type of system software that is needed to help maintain a

computer system. A basic set of utility programs is often supplied with the OS,

most of which help to manage files and their associated storage devices. However,

users can sometimes feel the need to get additional utilities which perhaps the

OS does not possess. Much of the work a computer does revolves around the use

of files of data so it is no surprise that it needs a number of programs that deal

with file handling. Without utility software, the computer would not function

properly. Utility software is required to manage the allocation of computer

memory in order to improve the computer’s performance and so that users can

customise the appearance of their desktop.

2.3.2Typesofutilitysoftware

The structure of hard disk storage

A hard-disk drive consists of several platters (individual disks) with each side

(surface) of the platter (top and bottom) having its own read–write head. The

read–write heads move across the platters, floating on a film of air and, when

they stop, they either read data from or write data to the surface. They never

touch the

disk surface and each surface is used to store data. The platters are

stacked one above the other and spin together at the same speed. Each surface is

divided into several tracks and each track is divided into sectors. The tracks are

2 HARDWARE AND SOFTWARE

in the same position on each disk. The track on the top platter together with the

tracks exactly below it, form a cylinder. Data is written to the platters starting

with the outside track. When a cylinder has been filled with data, the read–write

heads move toward the centre of the disk. They write data on each of the second

tracks until the second cylinder is full. The diagram just shows one track out of

the many that would be on the disk. There are normally 512 bytes of data in a

sector. Operating systems normally deal with data in

blocks. A block can consist

of one, two, four, eight or more sectors.

Track t

Sector s

Cylinder c

Platter

Rotation

Arm

assembly

Read–write head

Spindle

Arm

V Figure2.3Thestructureofhard-diskstorage

Formatting

Disk formatting is the configuring of a data storage medium such as a hard

disk or SSD for initial use. It can be performed on a disk that already has files

on it, but all those files would be erased. Disk formatting is usually carried out

on a new disk or on an existing disk if a new OS has to be installed. There are

two levels of formatting:

low-level formatting and high-level formatting.

Low-level formatting prepares the actual structure of the disk by dividing the disk

into cylinders and tracks and then dividing the tracks into sectors. This type of

formatting is usually carried out by manufacturers rather than individual users. If

users were to attempt this, there are at least two drawbacks: after erasing all the

files, it would be almost impossible to restore them and if done repeatedly, it would

shorten the life of the medium. When high-level formatting is carried out, it does

not permanently erase data files but deletes the pointers on the disk that tell the OS

where to find them. These pointers are in a File Allocation Table which is stored

on the disk and contains where the file starts and the length of the file. High-level

formatting is typically done to erase the hard disk and reinstall the OS back onto

the disk drive. Unlike low-level formatting, the files are retrievable. One benefit of

disk formatting is that it can remove viruses.

Disk defragmentation

When a file of data is stored on a disk, it may consist of several blocks. There

may not be enough blank or empty sectors next to each other to store all the

blocks together which means they have to be spread out across the disk. The file

is now said to be fragmented.

When data is no longer needed it is deleted from the disk, which leaves some

empty sectors.

Defragmentation software is used to organise the data on the

2.3 Utility software

disk by moving the data blocks around to bring all the parts of a file together so

they are contiguous. As a result, data retrieval is made easier and quicker. With

fragmented files it takes longer for the read–write heads to move over the surfaces

to find all the different fragments of files than if the data is held in sequence. In

addition, the software provides additional areas of free space and more storage

capacity. Sometimes it is impossible to bring all the blocks of data belonging to a file

together, but the software will move as many blocks together as possible. It can also

attempt to keep smaller files which belong in the same folder or directory together

by reorganising other files.

Data compression

Data compression is the modifying of data so that it occupies less storage

space on a disk. It can be lossless or lossy. Lossless compression is where, after

compression, the file is converted back into its original state, without the loss

of a single bit (binary digit) of data. When the lossless compression software

sees a repeated sequence of bits it replaces the repeated sequences with a special

character which indicates what is being repeated and how many times. This type

of compression is normally used with spreadsheets, databases and word-processed

files, where the loss of just one bit could change the meaning completely.

Lossy

compression permanently deletes data bits that are unnecessary, such as the

background in a frame of a video which might not change over several frames.

Lossy compression is commonly used with images and sound, where the loss

of some data bits would have little effect.

JPEG is an image file format that

supports lossy image compression. Formats such as GIF and PNG use lossless

compression. Other methods of file compression can be found in Chapter 11.

An advantage of data compression is that it means data can be transmitted more

quickly over a network or the internet. Another advantage is that it saves storage

space on a disk or SSD. Consequently, administrators spend less money and less

time on storage. It also allows the streaming of high definition (HD) videos

which would ordinarily occupy a great deal of bandwidth and memory.

There are disadvantages however, such as the fact that data compression

software uses a lot of computer memory during the compression process.

Another disadvantage is that the process of loading or opening a compressed file

takes a lot longer than opening the original. Also, lossy compression causes a

slight lowering of the quality of the resulting sound and video files.

Back-up

Back-up software is a program that is used to keep copies of files from a

computer or copy the content of a server’s backing storage. The back-up is an

exact duplicate of the files. It can be used for restoring the original files, should

the original files become corrupted or deleted, accidentally or deliberately. Back-

up software allows the user to select the time and type of back-up they want and

how regularly the back-up is to take place.

When tapes or external disk drives are used to store server back-ups, they are

normally stored in a room separate to the one where the server is housed.

Should a disaster occur with the server, such as fire or malicious damage, the

back-up tapes or disks are still safe. This is also the case where the Cloud is

used; damage to the server will not affect the state of the back-ups.

Most back-up software allows different types of back-up, not just a full back-up.

An incremental back-up is one where only the data that has been added or

changed since a specific date and time is backed up. Back-ups can take a long

2 HARDWARE AND SOFTWARE

time to carry out and require a certain amount of storage space, so this situation

is improved if back-ups are done incrementally. However, this can lead to

difficulties when restoring what may well be several back-ups. An alternative is

a differential back-up which only backs up the data which has changed since the

last full back-up. Restoring the system only requires the use of two back-ups in

this case. Users can also opt to verify their back-up; this is when checksums (see

Chapter 1) are used to make sure the data matches. Back-up software can also

allow the user to choose whether they want the back-up encrypted or not.

File copying

File copying is creating a duplicate copy of an existing file. The copy will

have exactly the same content as the original. There are a number of ways a

file-copying utility works. In disk operating systems, they tend to involve the

use of a command line interface (CLI) where the user types some form of

‘copy’ command which contains the name of the original file as well as the

destination directory or folder. With a

graphical user interface (GUI) the user

can have a variety of ways of doing this. One of the simplest is to have both

folder windows present on the screen and, using the mouse, right click over the

original file, select the Copy option from the drop-down menu, right click over

the destination folder, then select the Paste option from the drop-down menu.

There are now two versions of the same file in different folders.

Deleting

The delete utility is a piece of software which deletes the pointers that tell the

OS where to find the file. The OS now considers these sectors to be available for

the writing of fresh data. Until new data is written to the space the file occupies,

users can still retrieve the data. Data recovery software is available which allows

users to retrieve deleted data. It can identify the start and end of file markers

on the disk and reset the pointers accordingly. If, however, data has already

overwritten part of the file it will be extremely difficult, if not impossible, to

retrieve any of the data from the file.

The delete utility is not to be confused with pressing the delete button on the

keyboard. With some systems there is a trash folder and depending on the OS,

it may be called the recycle bin, trash or, simply, bin. When the delete button is

pressed the file is sent to this folder and files are stored there in case they need

to be retrieved.

Anti-virus

As the name suggests, anti-virus software can be a program or set of programs

whose function is to detect and remove viruses. It monitors a computer in a bid

to prevent attacks from many types of malware (malicious software) such as

viruses,

worms, Trojan horses, adware and many more. (The different types of

malware are described in detail in Chapter 5.) It is important to keep anti-virus

software up to date because new viruses and other types of malware appear at

frequent intervals and older versions of anti-virus will not detect these.

Anti-virus software will either remove the virus or malware or will quarantine

it, asking the user if they want to delete the file or ‘clean’ it. It can be set up

so that it scans specific files or folders for threats, as well as having the option

to scan the whole disk or the whole computer. Scans can be set up so that they

take place automatically and can be scheduled to take place at a specific time.

There are different methods employed by the anti-virus software to detect viruses.

One such method is

signature-based detection, which is based on recognising

2.4 Custom-written software and off-the-shelf software

existing viruses. When a virus is identified, anti-virus manufacturers add its

signature to a database of known viruses. This virus signature is a sequence of

bytes (remember, a byte is usually a string of 8 bits) contained within the virus

and this sequence will exist within any similar virus. The anti-virus checks all

files for this sequence of bytes and when discovered within a file, that file is

either deleted or quarantined. In essence, signature-based detection compares

the contents of a file with its database of known malware signatures. The main

drawback with this method is that it is only capable of dealing with known

threats. If a new virus is created, it will do untold damage to the software or data

stored on a hard disk because it is not within the known database. It was for this

reason that the

heuristic-based detection method, sometimes referred to as static

heuristic, was devised whereby a program is decompiled, its source code compared

to that of known viruses, and if a specific percentage matches, it is flagged as a

potential threat and quarantined. The drawback with this method is that a false

positive

can occur. This happens when the detection algorithm is so general that

matches can be made with files that do not contain viruses, but just happen to

contain a small part of the sequence of bytes which make up the virus.

Behavioural-based malware detection, sometimes referred to as the dynamic heuristic

method, looks for abnormal or suspicious behaviour, for example sending a large

number of emails or attempting to alter certain files. It too can generate false positives.

Sometimes

behavioural-based detection can be used in a sandbox environment.

This is a virtual environment within the computer whereby the suspected virus

infected code is executed in the sandbox, so that it can do no realharm.

Activity 2f

Write a sentence about each different type of utility software.

2.4 Custom-written software and

off-the-shelf software

When a company installs a new computer system, it will need to obtain

application software, whether it is for producing word-processed documents,

keeping databases of employee records or producing invoices. However, many

companies discover that finding the most appropriate software for them can

prove difficult. If a wrong decision is made, they may need to keep modifying

their system or even have to abandon the software and start again. Generally,

there are two choices: either buy

off-the-shelf software or ask someone to

create custom-written software.

2.4.1Custom-writtensoftware

This is software which has to be specially written for a particular task and is

developed for a specific company or business. If the company with the new

computer system is a large company, it might want to employ a programmer to

write software specifically to solve a particular problem or provide for a specific

need. There are reasons why it would want to do this. For example, it may need

databases to be designed which require specialist programming skills. It may

also need a website to be created which it wants to have tailored to its own

needs. Once the software is written, the company will own it and may be able to

sell it to other companies.

2 HARDWARE AND SOFTWARE

2.4.2 Off-the-shelf software

This is software which already exists and is available straight away, ready for use. If the

company with a new computer system is a smaller company, it may turn to one of the large

software companies that already produce business software packages, for example invoicing

software, accounting software, payroll software and other programs which are available to

all businesses, organisations and the general public. Such programs may provide features

that many users want, such as text editing, accounting functions and mail merge. The

drawback is that in trying to cater for a wide range of users, there may be a substantial

number of features that the purchasing company does not need, such as trigonometric

functions or engineering functions. The software may therefore need to be adapted for

the company’s own specific purpose, which can mean that it occupies a large amount of

storage space. Unlike custom-written software, it will not be owned by the purchasing

company and even if adapted for it, it will not be able to sell it to other companies.

2.4.3 Advantages and disadvantages of custom-written and

off-the-shelf software

Here is a table showing custom-written software compared to off-the-shelf software.

Notice how each paragraph contains comparisons.

Advantages of custom-written software Disadvantages of custom-written software

Custom-written software is designed specifically

for the task and will meet all the customer’s

requirements. It will not need to be adapted,

unlike off-the-shelf software, which may be

difficult to adapt to the particular use the

customer requires.

The customer will have to pay the programmers to write the

programs which have to be written specifically for the task and this

will cost more than if they were buying off-the-shelf software. Off-

the-shelf software is cheaper to buy because it is mass-produced.

Instead of one customer paying for the development there are

several customers paying the software company and thereby

indirectly contributing to the development costs.

If the software does not quite meet what the

customer wants, alterations to the software can be

made by the programmer who is readily available.

Because there will only be one programmer or a small team of

programmers, customers may find it difficult to get support if

anything goes wrong. With off-the-shelf software, there are

likely to be internet forums or websites to help users, as well as

telephone helplines with operators who will be experienced with

all sorts of queries other customers have made.

Off-the-shelf software may have some features

which are not necessary for the customer, but

custom-written software will not have any

unnecessary features. Off-the-shelf software may

not have all the functions the customer needs, but

the programmer will make sure these are included

in custom-written software.

It can take a long time to develop the software since the

programmers will be starting from scratch, whereas

off-the-shelf software is available immediately because it has

already been written. There is also the likelihood that a lot of

time will be spent having meetings with the programmers to tell

them what will be required of the system.

The programmers will know what the current

computer system is and will be able to make sure

that the software is compatible with it, unlike off-

the-shelf software which may not necessarily be

compatible with the hardware or operating system

currently being used. There may be settings within

the off-the-shelf software that cannot be changed.

There may be more bugs in custom-written software as it may not

have been tested as thoroughly. Often the tests that are carried

out are those which the programmer thinks are necessary based

on how they think the software will be used, which may not be

accurate. Off-the-shelf software is usually tested rigorously so it

is highly unlikely that there will be any bugs in it and it will have

been used many times already, so any bugs that were present will

have been discovered and removed.

The customer will own the copyright of the custom-

written software and so be able to sell it to others

and have extra income. With off-the-shelf software,

even if they adapt it, customers cannot sell it as this

would infringe the software company’s copyright.

V Table 2.2 Advantages and disadvantages of custom-written software and off-the-shelf software

2.5 User interfaces

Proprietary and open source software will be described in Chapter 10,

Section 10.12.

Activity 2g

Describe custom-written software and off-the-shelf software in terms of:

a availability

b number of bugs.

2.5 User interfaces

A user interface is the means by which the computer system interacts with the

user. It enables the user, with the help of input devices, to communicate with the

computer and then, via the OS, communicate with a piece of software or any

output device. A good user interface is one which allows the user to perform this

communication without encountering any problems; it needs to be user-friendly.

It should also be intuitive; users should be able to predict what will happen if

they take a certain action, for example if a button on a user interface looks like

a button in real life (such as the on/off button on a computer), a user should be

able to press it and get a response. The four major interfaces are the

command

line interface, graphical user interface, dialogue interface and gesture-based

interface.

2.5.1 Command line interface

The command line interface (CLI) is a means of interacting with a computer using

commands in the form of successive lines of text. Normally, a prompt appears on

the screen to which the user responds by typing a command. The output from the

computer could be to produce a list or take some other action. In the early days

of computing, the CLI was the only way a user could get the computer to run

software or carry out tasks. This type of user interface is rarely used today except

by software developers, system administrators and more advanced users. Most

individuals use a graphical user interface (GUI) when communicating with their

computers. However, even within a GUI it is still possible to access a CLI.

V Figure2.4Acommandlineinterfacescreen

2 HARDWARE AND SOFTWARE

As we can see in Figure 2.4, the CLI usually consists of a black box with white

text. In the early days of computing the text was green. In Figure 2.4, on entering

the interface, a prompt C:\Users\guest_8k65j6c> appears. The > symbol tells

the user that they need to type in a command. Here, the command ‘dir’ was

entered, which asked the computer to list the files and directories (folders) that are

in the directory (folder) belonging to the user guest_8k65j6c. Notice that after

executing the command, the original prompt is shown again. In this example

there are no files in this directory, only other directories. The ‘dir’ command is

only one of hundreds of commands which are available in a CLI. It is possible to

do any action with a CLI that could be achieved with a GUI. In fact, it could take

several clicks of the mouse and negotiation through a number of dialogue boxes

and menus in a GUI to achieve the same outcome as a single line of text in a CLI.

2.5.2 Graphical user interface

Icons

Window

V Figure2.5Agraphicaluserinterfacescreen

When CLIs were introduced, commands had to be typed in correctly with any

misspellings potentially causing the system to fail to perform as desired, and this

made the interface clumsy and confusing. There was a need for a less inefficient

means of communicating with the computer, which resulted in the creation of the

GUI. Instead of typing in commands, the GUI used windows, icons, menus and

pointers, collectively known as a ‘WIMP’ interface, to carry out commands, such as

opening, deleting, and moving files. Technically speaking, a WIMP interface is only

a subset of GUI and requires input devices such as a keyboard and mouse, whereas

other types of GUI use different input devices such as a touchscreen. Figure 2.5

shows a window, icons and a menu. A user can double-click on an icon, which could

represent a file, a folder or an application, and open it. A right click on a two-button

mouse opens a menu. By moving the mouse, the pointer can be moved up and

down through the menu and then an option can be selected by clicking on it.

2.5.3 Dialogue interface

A dialogue interface allows a user to communicate with a computer or device using

their voice. The computer is able to use speech-recognition software to convert

2.5 User interfaces

the spoken word into commands it can understand. Many cars have such a system

whereby the driver is able to control their phone or radio without touching them.

For example the driver is able to initiate a phone call by saying ‘phone Graham’ or

switch a particular radio channel on by saying the name of the channel. Laptops

and PCs often come with voice control these days. The user is able to load and

run software packages and files by speaking into a microphone and saying the

commands. The computer or device responds with spoken words after the required

text has been converted into speech. It requires the device to learn the way the

speaker talks by asking the user to repeat certain sentences until it has ‘learnt’ the

way they speak. It can, however, become quite capable of understanding simple

commands. Noise in the background while the user is speaking and the ability to

recognise only a limited vocabulary can cause problems.

2.5.4 Gesture-based interface

A gesture-based interface is designed to interpret human gestures and convert

these into commands. Gestures can be made with any part of the body, but it

is usually the face or hand that makes the gestures the computer can interpret.

An example of where this type of interface is used is in ‘smart’ homes where

a gesture can turn on the lights, for example. In this area of IT, a gesture can

be said to be any physical movement, large or small, that can be interpreted

by a computer. Examples of these are the pointing of a finger, nodding the

head, or a wave of the hand. These types of gestures can be understood by a

computer. First of all, a camera in conjunction with an infrared sensor detects

the movements being made in front of it. The computer, using a special type

of software, searches through all the gestures it has stored in a database to

match it with the input. Each stored gesture is linked to a specific command

which is then executed after the gesture has been matched.

2.5.5 Advantages and disadvantages of different types

of user interface

Users with disabilities may not be able to hold a mouse or click it, so a GUI

may not be suitable for them. They may not be able to type using a keyboard,

so using a CLI would also be inappropriate. They may not be able to control

the movement of their limbs accurately, so a gesture-based interface would be

unsuitable. In this instance, then, a dialogue interface would be the best type of

interface for them to use, although people with different disabilities may favour

a different type of user interface.

Despite this potential advantage of a dialogue interface, if there is

any background noise when the user is speaking, the computer might

misunderstand what is being said, which is not a problem when using the other

types of interface.

Some types of user interface would be inappropriate for hygienic reasons. If

a user was, for example, involved in the food service industry, then touching

a mouse, keyboard or touchscreen may be inadvisable while working, so a

GUI or CLI would not be suitable for them. However, they would be able

to make gestures and speak, so a gesture-based or dialogue interface would

be a sensible choice for them. On the other hand, certain gestures could

be misunderstood by the computer, particularly if the user has made them

without realising, and some gestures in certain cultures might be judged to

be inappropriate.

2 HARDWARE AND SOFTWARE

In terms of accuracy, a GUI is better than gesture-based or dialogue interfaces.

A gesture may not point exactly at an icon whereas a mouse can be more

accurately controlled, and voice inputs can be misunderstood by the speech-

recognition software.

CLIs and, to an extent, dialogue interfaces require the user to learn a lot of

commands, whereas GUIs and gesture-based interfaces are more user-friendly

and reasonably intuitive. CLIs do tend to be used by IT specialists and require a

certain amount of IT knowledge but this is not the case with GUIs or gesture-

based interfaces. Compared with a GUI, commands entered into a CLI are

far more difficult to correct. There is a degree of editing allowed using the

arrow keys on a keyboard to manoeuvre to the line with the error, but this can

be far more awkward to do than using a mouse, for example. However, CLIs

tend not to change over time and once a user is familiar with one, they do not

have to relearn how to use a changed version. GUIs do tend to develop and

consequently the user has to learn how to use the new version, which can take

time.

Generally, the more advanced the type of interface, and this not only means

GUIs but also includes gesture-based and dialogue interfaces, the faster the

processing is and the greater the storage space required to store the interface

software compared with a CLI. Gesture-based and dialogue interfaces also

tend to be more expensive to develop than CLIs or even GUIs. Some situations

require the use of dialogue interfaces for safety reasons. A driver in a vehicle may

wish to play a particular piece of music using their in-car entertainment system.

To select it using a GUI or a gesture would require taking a hand off the

steering wheel, which could be dangerous, whereas using their voice through a

dialogue interface would not.

Activity 2h

1 Write down two advantages of using a GUI rather than a CLI.

2 Write down two disadvantages of using a gesture-based interface rather

than a dialogue interface.

Examination-style questions

1 Mainframe computer manufacturers often refer to RAS.

Explain what is meant by the term ‘RAS’.

[3]

Explain how high-level language is translated to run on different

computer systems.

[5]

Describe the terms: [4]

sector

b block

c track

d cylinder.

4 Explain what is meant by custom-written software. [3]

Describe the features of a command line interface. [4]