Section Two: System Software

Question 1

Chapter 7 – Functions of an operating system
What is a operating system?

Answer 1

A program or set of programs that manages the operations of the computer for the user. It acts as a bridge between the user and the computer’s hardware, since a user cannot
communicate with hardware directly.

Question 2

Chapter 7 – Functions of an operating system
What are the function of an operating system?

Answer 2

Apart from providing a user interface, the operating system has to perform the following functions:
- Memory management
- Interrupt service routines
- Processor scheduling
- Backing store management
- Management of all input and output

Question 3

Chapter 7 – Functions of an operating system
What is memory management?

Answer 3

The process of controlling and coordinating a computer’s main memory. It ensures that blocks of memory space are properly managed and allocated so the operating system (OS), applications and other running processes have the memory they need to carry out their operations

Question 4

Chapter 7 – Functions of an operating system
What is paging?

Answer 4

Paging is when​ memory is split up into equal-sized sections known as pages​. These can then be swapped between main memory and the hard disk​ as needed. Segmentation is the ​splitting up of memory into logical sized divisions​, known as segments, which vary in size.

Question 5

Chapter 7 – Functions of an operating system
What is segmentation?

Answer 5

Segmentation is the logical division of address space into varying length segments which depend on
the program structure. As with paging, it is possible to load only a part of a program into memory initially.

Question 6

Chapter 7 – Functions of an operating system
What is Virtual Memory?

Answer 6

Virtual memory is a section of volatile memory created temporarily on the storage drive. It is created when a computer is running many processes at once and RAM is running low

Question 7

Chapter 7 – Functions of an operating system
What are Interrupts?

Answer 7

An interrupt is a signal from a software program, hardware device or internal clock to the CPU. A software interrupt occurs when an application program terminates or requests certain services from the operating system. A hardware interrupt may occur, for example, when an I/O operation is complete or an error such as `Printer out of paper’ occurs.

Question 8

Chapter 7 – Functions of an operating system
What are Interrupt service routines?

Answer 8

A set of instructions that have to be carried out when the event occurs. For example, a typical algorithm for handling the mouse might be: Mouse moves. A hardware chip on the Motherboard, called the ‘interrupt controller’, detects the mouse signal.

Question 9

Chapter 7 – Functions of an operating system
What is processor scheduling?

Answer 9

The process of removing an active task from the processor and replacing it with a new one. It divides a procedure into states such as ready, waiting, or running.

Question 10

Chapter 7 – Functions of an operating system
The objectives of the scheduler

Answer 10

• Maximise throughput
• Be fair to all users on a multi-user system
• Provide acceptable response time to all users
• Ensure hardware resources are kept as busy as possible

Question 11

Chapter 7 – Functions of an operating system
What is round robin?

Answer 11

the Round Robin scheduling algorithm, a queue is made holding all processes that are ready to run. When the first process is loaded into main memory, it is given a set amount of CPU time to use. If the process is completed during the allocated time then the next process in the queue is loaded immediately. However, if the process is not finished when its time expires, it is put at the back of the queue to wait for another turn

Question 12

Chapter 7 – Functions of an operating system
What is Backing store management?

Answer 12

When files and applications are loaded, they are transferred from backing storage into memory. The operating system is required to keep a directory of where files are stored so that they can be quickly accessed. The file management system that comes with your desktop operating system enables a user to move files and folders, delete files and protect others from unauthorised access.

Question 13

Chapter 7 – Functions of an operating system
What is peripheral management

Answer 13

Operating systems are responsible for ‘ peripheral management ‘ this means. They communicate and control devices such as mice, keyboards, monitors and printers. This can include sending print jobs to the printer

Question 14

Chapter 8 – Types of operating system
What is a Distributed operating systems?

Answer 14

A distributed operating system is a form of parallel processing system which spreads the load over multiple computer servers. A single job is split up into several tasks and each of these is run on a separate computer, coordinated by the operating system, in such a way that it appears to a user to be
a single system.

Question 15

Chapter 8 – Types of operating system
What is a multi-tasking system?

Answer 15

A multi-tasking operating system may run on a standalone computer such as a PC or laptop. The Windows operating system, for example, can run many jobs simultaneously, switching between them so that each one appears to be the only one running.

Question 16

Chapter 8 – Types of operating system
What is a multi-user, multi-tasking system

Answer 16

Time-sharing systems are multi-user, multi-tasking systems. A single powerful mainframe or supercomputer is connected to dozens or hundreds of terminals all using the mainframe CPU. Each user gets a slice of processor time according to a scheduling algorithm,

Question 17

Chapter 8 – Types of operating system
What is a operating systems used by mobile phones?

Answer 17

A mobile phone is a multi-tasking computer that has its own operating system. Operating systems used on smartphones, tablets, PDAs and other mobile devices are termed mobile operating systems. They combine the features of a personal computer operating system with their own special features
useful for mobile use such as managing cellular and wireless connectivity as well as phone access.

Question 18

Chapter 8 – Types of operating system
What is an embedded operating systems?

Answer 18

Embedded systems are found in all kinds of hardware from a washing machine or microwave oven, to the control system of a passenger aircraft or a space shuttle.

Question 19

Chapter 8 – Types of operating system
The main features of embedded operating systems

Answer 19

• it will have a minimal user interface, probably consisting of a few buttons or a dial and maybe a small screen
• it will accept input from sensors, and send output to control devices
• there is a limited amount of RAM so a complex memory management system is not required
• there will not be any permanent data storage devices to be managed

Question 20

Chapter 8 – Types of operating system
What is a BIOS(Basic Input Output System)?

Answer 20

BIOS is the program stored in EPROM (Erasable Programmable Read-Only Memory) that gets your
computer started after you turn it on. The fundamental purpose of BIOS in modern PCs is to initialise and test the system hardware components and to load the operating system (or the key parts of it) from the hard disk into RAM.

Question 21

Chapter 8 – Types of operating system
What is a device drivers?

Answer 21

A device driver is a computer program that provides a software interface to a particular hardware device.
This enables operating systems to access hardware functions without needing to know the details of the hardware being used. When you attach a new printer to your computer, for example, you will have to install the device driver program that comes with it before it will work.

Question 22

Chapter 8 – Types of operating system
What is a virtual machine?

Answer 22

A virtual machine can be defined as any instance where software is used to take on the function of the machine, including executing intermediate code or running an operating system within another to emulate different hardware.

Question 23

Chapter 9 – The nature of applications
Classification of software

Answer 23

Software can be broadly classified into systems software and applications software.

Question 24

Chapter 9 – The nature of applications
What is systems software?

Answer 24

System software is the software needed to run the computer’s hardware and application programs. This includes the operating system, utility programs, libraries and programming language translators. Libraries and programming language translators will be considered in the next chapter.

Question 25

Chapter 9 – The nature of applications
What is a Operating system?

Answer 25

The OS is a set of programs that lies between applications software and the computer hardware, and has many different functions

Question 26

Chapter 9 – The nature of applications
Function of a OS

Answer 26

• resource management – managing all the computer hardware including the CPU, memory, disk drives, keyboard, monitor, printer and other peripheral devices
• provision of a user interface (e.g. Windows) to enable users to perform tasks such as running application software, changing settings on the computer, downloading and installing new software, etc.

Question 27

Chapter 9 – The nature of applications
What are Utility programs?

Answer 27

Utility software is system software designed to optimise the performance of the computer or perform tasks such as backing up files, restoring corrupted files from backup, compressing or decompressing data, encrypting data before transmission, providing a firewall, etc.

Question 28

Chapter 9 – The nature of applications
What is Disk defragmentation?

Answer 28

A disk defragmenter is a program that will reorganise a magnetic hard disk so that files which have been split up into blocks and stored all over the disk will be recombined in a single series of sequential blocks. This makes reading a file quicker.

Question 29

Chapter 9 – The nature of applications
What are Automatic backups?

Answer 29

Several free automatic backup utilities are available for personal and commercial use. An automatic backup utility will allow the user to specify
- Where you want to store the backup (the destination)
- What you want to backup (the sources)
- How you want to run the backup (using full backup that zips the files, or mirror backup that doesn’t zip them)
- When you want to run the backup (you can schedule it to run automatically or run it manually)

Question 30

Chapter 9 – The nature of applications
What are automatic updating?

Answer 30

An automatic update utility makes sure that any software installed on the computer is up-to-date. For any software already installed on the computer, the automatic update utility will regularly check the Internet for updates. These will be downloaded and installed if they are newer than the version already on the computer.

Question 31

Chapter 9 – The nature of applications
What is a Virus checker?

Answer 31

A virus checker utility checks your hard drive and, depending on the level of protection offered, incoming emails and internet downloads, for viruses and removes them.

Question 32

Chapter 9 – The nature of applications
What is a Compression software?

Answer 32

Several utility programs are supplied as part of the operating system. These include utilities to copy, move and delete files, create, move and delete folders, provide screensavers. Other utility programs such as WinZip for compressing and sharing files have to be purchased from independent suppliers.

Zipped or compressed files can be transmitted much more quickly over the Internet. Sometimes there is a limit to the size of a file which can be transmitted

Question 33

Chapter 9 – The nature of applications
What is application software?

Answer 33

Applications software can be categorised as general-purpose, special-purpose or custom-written(bespoke) software.

Question 34

Chapter 9 – The nature of applications
What is General-purpose software?

Answer 34

General-purpose software such as a word-processor, spreadsheet or graphics package, can be used for many different purposes. For example, a graphics package may be used to produce advertisements or animations, manipulate photographs, draw vector or bitmapped images.

Question 35

Chapter 9 – The nature of applications
What is Special-purpose software?

Answer 35

Special-purpose software performs a single specific task or set of tasks. Examples include payroll and accounts packages, hotel booking systems, fingerprint scanning systems, browser software and hundreds of other applications. Software may be bought “off-the-shelf”, ready to use, or it may be specially written by a team of programmers for a particular organisation.

Question 36

Chapter 9 – The nature of applications
“Off–the-shelf” vs bespoke software

Answer 36

Off the self
- Less expensive since the cost is shared among all the other people buying the package
- May contain a lot of unwanted features, and some desirable but non-essential features may be missing
- Ready to be installed immediately
- Well documented, well-tested and error-free

Bespoke software
- More costly and requires expertise to analyse document requirements
- Features customised to user requirements and other features can be added as needs arise
- May take a long time to develop
- May contain errors which do not surface immediately

Question 37

Chapter 9 – The nature of applications
What is open source?

Answer 37

Open Source software is governed by the Open Source initiative that says:
- Software is licensed for use but there is no charge for the licence. Anyone can use it.
- Open Source software must be distributed with the source code so anyone can modify it.
- Developers can sell the software they have created.
- Any new software created from Open Source software must also be “open”. This means that it must be distributed or sold in a form that other people can read and also edit.

Question 38

Chapter 9 – The nature of applications
What is close source?

Answer 38

Closed source or proprietary software is sold in the form of a licence to use it.
- There will be restrictions on how the software can be used, for example the licence may specify only one concurrent user, or it may permit up to say, 50 users on one site (site licence).
- The company or person who wrote the software will hold the copyright. The users will not have access to the source code and will not be allowed to modify the package and sell it to other people. This would infringe the copyright (Copyright, Designs and Patents Act).

Question 39

Chapter 10 – Programming language translators
What is an Assembly code?

Answer 39

Assembly code is a low level language, with each instruction in assembly code almost always being equivalent to one machine code instruction. The machine code instructions that a particular computer can execute (the instruction set) are completely dependent on its hardware, and therefore each different type of processor will have a different instruction set and a different assembly code.

Question 40

Chapter 10 – Programming language translators
What is an Assembler?

Answer 40

Before an assembly code program can be executed, it must be translated into the equivalent machine code. This is done by a program called an assembler. The assembler program takes each assembly code instruction and converts it to the 0s and 1s of the corresponding machine code instruction. The input to the assembler is called the source code and the output (machine code) the object code.

Question 41

Chapter 10 – Programming language translators
What is a Compiler?

Answer 41

A compiler is a program that translates a high-level language such as Visual Basic, Python etc. into machine code. The code written by the programmer, the source code, is input as data to the compiler, which scans through it several times, each time performing different checks and building up tables of information needed to produce the final object code.

Question 42

Chapter 10 – Programming language translators
What is an Interpreter?

Answer 42

An interpreter is a different type of programming language translator. Once the programmer has written and saved a program, and instructs the computer to run it, the interpreter looks at each line of the source program, analyses it and, if it contains no syntax errors, translates it into machine code and runs it.

Question 43

Chapter 10 – Programming language translators
What is Bytecode?

Answer 43

Bytecode is source code that has been compiled into low-level code (bytecode) designed to be run on a virtual machine (the interpreter). An interpreter must be present on the user’s computer for the bytecode to be translated and executed

Question 44

Chapter 10 – Programming language translators
Advantages and uses of compilers

Answer 44

A compiler has many advantages over an interpreter:
- the object code can be saved on disk and run whenever required without the need to recompile. However, if an error is discovered in the program, the whole program has to be recompiled
- the object code executes faster than interpreted code
- the object code produced by a compiler can be distributed or executed without having to have the compiler present
- the object code is more secure, as it cannot be read without a great deal of ‘reverse engineering’

Question 45

Chapter 10 – Programming language translators
Advantages and uses of interpreters

Answer 45

An interpreter has some advantages over a compiler:
- platform independence - the source code can be run on any machine which has the appropriate interpreter available (e.g. java’s byte code)
- it is useful for program development as there is no need for lengthy recompilation each time an error is discovered

Question 46

Chapter 10 – Programming language translators
Disadvantages of an interpreter

Answer 46

The program may run slower than a compiled program, because each statement has to be translated to machine code each time it is encountered. So if a loop of 10 statements is performed 20 times, all 10 statements are interpreted 20 times.

Question 47

Chapter 10 – Programming language translators
Stages of compilation

Answer 47

There are three stages of compilation: lexical analysis/syntax analysis, and code generation and optimisation.

Question 48

Chapter 10 – Programming language translators
What is the Lexical analysis?

Answer 48

1. Removal of any non-program elements(Comments should be used to help explain complex parts of the code. While white space and comments are helpful for the human reader, they are not necessary for the executable code, so the compiler removes them during lexical analysis.)
2. Tokenisation(Once the non-program elements have been removed, the characters are read and each string is analysed)

Question 49

Chapter 10 – Programming language translators
What is a symbol table?

Answer 49

As part of the lexical analysis stage, a symbol table is produced. A symbol table is used by the compiler to keep track of all of the identifiers that have been declared in the program

Question 50

Chapter 10 – Programming language translators
What will the symbol table show?

Answer 50

• the identifier or keyword
• the kind of item (variable, array, procedure, keyword etc.)
• the type of item (integer, real, char etc.)
• the run-time address of the item, or its value if it is a constant
• a pointer to accessing information (e.g. for an array, the bounds of the array, or for a procedure, information about each of the parameters).

Question 51

Chapter 10 – Programming language translators
Syntax analysis

Answer 51

Syntax analysis is the process of determining whether the sequence of input characters, symbols, items or tokens form a valid sentence in the language. In order to do this, the language has to be expressed as a set of rules, using for example syntax diagrams or Backus-Naur form.

Question 52

Chapter 10 – Programming language translators
Semantic analysis

Answer 52

The semantics of the program will also be checked in this phase. Semantics define the meaning rather than the grammar of the language; it is possible to write a series of syntactically correct statements which nevertheless do not obey the rules for writing a correct program. An example of a semantic error is the use of an undeclared variable in Pascal, or trying to assign a real value to an integer variable, or using a real number instead of an integer as the counter in a for … next loop.

Question 53

Chapter 10 – Programming language translators
Code generation and optimisation

Answer 53

Code optimisation techniques attempt to reduce the execution time of the object program by, for example, spotting redundant instructions and producing object code which achieves the same net effect as that specified by the source program but not by the same means.

Question 54

Chapter 10 – Programming language translators
Linkers and loaders

Answer 54

Once a program has been compiled, any separately compiled subroutines must be linked into the object code. These may be input or output routines, routines such as a random number generator or timer routine which are supplied with the language, or routines written by the programmer and held on disk in a library of subroutines. It is the job of the linker to put the appropriate machine addresses in all the external call and return instructions, so that the modules are linked together correctly.

A relocating loader can load the object code anywhere in memory, provided the programmer has used no
absolute addresses and the object code is in relocatable format.

Question 55

Chapter 10 – Programming language translators
Use of libraries

Answer 55

Library programs are ready-compiled programs which can be run when needed, and which are grouped together in software libraries. In Windows these often have a .dll extension. Most compiled languages have their own libraries of pre-written functions which can be invoked in a defined manner from within the user’s program.

Question 56

Chapter 10 – Programming language translators
Advantages of library routines
Most programming languages have extensive libraries of built in functions such as chr(), ascii(), sqrt() etc. They also have libraries of modules that provide solutions to common problems in everyday programming, such as mathematical functions, generating random numbers in a specified range,
providing a graphical user interface. These libraries can be imported into a user’s program and have
many advantages including:
* they are tested and error-free
* they save the programmer time in “re-inventing the wheel” to write code themselves to perform
common tasks