Systems software and software development

Question 1

State functions of OS

Answer 1

Memory management (paging, VM, allocating memory etc.)
Provide a (user) interface
Manage hardware/peripherals
Manage CPU usage / handles interrupts
Provide system security
Provide platform to run other software
Provide utilities for system maintenance

Question 2

What is virtual memory

Answer 2

Memory content divided into pages
Pages not needed get moved to VM
VM is an area on a secondary storage device
When required, pages are moved from VM back into RAM

Question 3

What is paging

Answer 3

Paging is fixed size / physical divisions (units)

Question 4

What is segmentation

Answer 4

Segmentation is dividing memory logically (variable size)

Question 5

What is an interrupt

Answer 5

A signal to the processor indicating a device/process needs attention

Question 6

Describe the process of receiving interrupts

Answer 6

-Complete current FDE cycle
-Check priority of incoming interrupt
-If it’s a higher priority than the current task…
-…contents of registers are stored in memory…
-…in a stack
-…relevant interrupt service is loaded
-… by changing PC to memory location of ISR
-…when ISR (Interrupt Service Routine) has completed, the previous state is popped from the stack…
-…and loaded back into registers

Question 7

State the scheduling algorithms

Answer 7

First come first served
Round Robin
Multi-level feedback queues
Shortest job first
Shortest time remaining

Question 8

When is the scheduling algorithm “first come first served” suitable

Answer 8

When jobs are dispatched FIFO, jobs are equal priority and equal processing time

Question 9

What is open source software

Answer 9

Source code is freely available, for others to amend

Question 10

Explain an advantage of using open source software for a company

Answer 10

A lot of the core functionality needed is already available, so the company just has to make amendments/additions specific to their system, saving time and money

Question 11

What is closed source software

Answer 11

Closed source software is distributed in binary form only/source code is not freely available, and there are licensing conditions restricting the redistribution/no permission to amend program

Question 12

State the disadvantages of custom-written software

Answer 12

Wait time is long, large cost, help not easily available (no user community), has not been trial and tested, there are likely to be other off-the-shelf alternatives

Question 13

What is RTOS

Answer 13

Processor will make decisions based on changes and take action immediately (within a small fraction of a second)

Question 14

What is an advantage of RTOS over non-RTOS, stating an

Answer 14

RTOS gives a guaranteed response time
Non-RTOS might be busy might be busy dealing with other tasks and may respond once it’s too late
Needed in systems which need to respond to changes immediately, such as in self-driving cars (eg. person steps in front of car)

Question 15

What is an embedded system

Answer 15

Software used to manage device
Which is built into the device itself
Stored in device’s ROM so cannot be changed
Specific to hardware/purpose

Question 16

What is a distributed OS, and what tasks might it be used for

Answer 16

Allows multiple computers to work together on a single task
Used for computationally intensive tasks (textbook)

Question 17

What is a multitasking OS

Answer 17

Can run multiple programs simultaneously

Question 18

What is a multi-user OS

Answer 18

Allows multiple users to use a system and its resources simultaneously (this does not mean just allowing multiple accounts)

Question 19

What is a virtual machine

Answer 19

A piece of software that behaves in the same way as an actual computer.
A theoretical computer which provides an environment in which a translator is available
Uses an interpreter to run intermediate code

Question 20

State the advantages of virtual machine

Answer 20

-reduced hardware costs
-improved security by keeping all software running from one physical device
-easier/cheaper to manage as only one physical device runs programs
-can add/remove resources
-no direct access to hardware
-resources can be used more flexibly between the machines

Question 21

What is intermediate code

Answer 21

Is simplified code that…
…is between high level & machine code
…is produced by compiler
…runs on any computer
…allows portability between machines
Not machine code, cannot be read by CPU, but still a similarly efficient representation of a program. Any device running appropriate VM can read this intermediate code, while machine code is hardware specific (textbook)

Question 22

State advantages of intermediate code

Answer 22

Allows sections of code to be written in different languages…
…by different programmers
…suitable for specific tasks
Error free
Protects source code

Question 23

What is an assembler

Answer 23

A program that translates assembly code into machine code/object code
Useful for developers

Question 24

What is a compiler

Answer 24

A program that translates high level language into hardware specific machine code/object code.
Creates an executable file and compiles the whole program at once, and returns all the errors (not MS)

Question 25

Stages of compilation AO1

Answer 25

Compiler is effectively a group of programs Lexical analysis, syntax analysis, code generation and optimisation Linker used to combine object code with the library code to make the final executable

Question 26

Stages of compilation, first stage AO2

Answer 26

Source code is inputted into compiler program First stage is lexical analysis in which… …comments and whitespace are removed …variables and subroutines are stored in a symbol table …which also holds data such as scope and data type …code is converted into a series of tokens Series of tokens and symbol table is passed onto the next stage, syntax analysis…

Question 27

Stages of compilation, second stage AO2

Answer 27

…code is checked to ensure that it follows the rules of the language …errors are generated (reported as a list) when rules are broken If no rules are broken, it is passed onto code generation…

Question 28

Stages of compilation, third stage AO2

Answer 28

…object/machine code is created …may be inefficient …main program source code will have contained lines importing the library code …a program called a linker can incorporate the code from the library with the main program …into a single executable program

Question 29

Stages of compilation AO3

Answer 29

Lexical analysis necessary to put code into format which can be read and processed by a syntax analyser Syntax analysis is necessary to ensure code meets all structural rules of the language, so guaranteeing it will run, though maybe not as expected Code generation is necessary to turn code into a format that the processor can understand Optimisation is not necessary, but improves efficiency Linking is necessary to ensure library code is incorporated into the final program

Question 30

What are linkers

Answer 30

A linker links the main program to software libraries (1) by either including them in the final executable code (1) or by getting the executable code to point to the external libraries (1) to form a single executable file (1)

Question 31

What are loaders

Answer 31

Part of the operating system Loads an executable file into memory… …from secondary storage Loads the required software libraries

Question 32

What are libraries

Answer 32

Libraries are ready compiled programs (1), grouped in software libraries (1) which can be loaded and run whenever (1)

Question 33

What are advantages of libraries?

Answer 33

Advantages of libraries: saves time/money as it is prewritten, draws on expertise of other programmers, pre-tested, can have been written in a different language

Question 34

What are disadvantages of libraries

Answer 34

Disadvantages: may increase size of compiled file as library contains many routines that aren’t being used, not written by the programmer so introduces uncertainty

Question 35

Compiler > Interpreter

Answer 35

Object code can be saved on a disk and run whenever required without need to recompile Object code executes faster than interpreted code Object code can be distributed or executed without compiler present Object code is more secure, cannot be read without a great deal of reverse engineering

Question 36

In what situation is a compiler appropriate

Answer 36

Overall, compilers are appropriate when a program is run regularly, with occasional change. Also if distributed / sold since the source code is not present

Question 37

Interpreter > Compiler

Answer 37

Platform independence (source code can be run on any machine with appropriate interpreter) Useful for program development, no need for lengthy recompilation each time error is discovered

Question 38

Define utility software

Answer 38

Utility software performs a specific task usually related to the upkeep of a system

Question 39

File management purpose and uses

Answer 39

Purpose - manages/organises data storage Uses - moving/deleting files/folders, manage storage of software/allows access to files

Question 40

Hardware drivers purpose and uses

Answer 40

Purpose - software that allows for communication between the operating system and hardware device (peripheral) Uses - to configure hardware, used to install a new keyboard, mouse etc.

Question 41

Backup utilities purpose and uses

Answer 41

Purpose - automatically makes copy of files, storing them in a different location in case of loss/corruption Uses - to make incremental backups

Question 42

Disk defragmenter purpose and uses

Answer 42

Purpose - will reorganise a magnetic hard disk so that files which have been split up blocks and stored all over the disk will be recombined into a single series of sequential blocks Uses - makes reading a file more rapid relatively

Question 43

Difference between system software and application software

Answer 43

System software controls the hardware (eg. any function of OS) Application software allows the user to do something useful, complete a specific task

Question 44

Assembly modes of addressing

Answer 44

Direct Indirect Immediate Indexed

Question 45

Use cases for assembly language

Answer 45

Quicker / more efficient to translate Makes more efficient use of CPU/memory/system resources Gives programmer direct control over hardware/memory Code might be written for a specific architecture Compilers/interpreters may not be available

Question 46

Assembly vs high level

Answer 46

Assembly language uses mnemonics ● HLL uses English-like words Assembly language uses an assembler to convert to machine code ● HLL uses a translator (compiler/interpreter) to convert to machine code Assembly language is a one-to-one conversion to machine code ● HLL may produce multiple lines of machine code per line of code // one-to-many Assembly language requires more knowledge of the processor // allows direct control of the processor ● HLL provides more abstraction // requires less knowledge of the processor Assembly language is likely to be specific to the processor type used // is machine dependent ● HLL is portable // is machine independent

Question 47

Briefly describe the structure of assembly code

Answer 47

Three columns: labels, opcode, operand Uses mnemonics

Question 48

Extreme programming

Answer 48

The programming stage is the main focus / priority Is a form of agile development Includes planning, design, code, test Testing is focused throughout development Prioritises code quality... ... over documentation Encourages the use of pair programming

Question 49

Waterfall lifecycle

Answer 49

Includes analysis, design, implementation/programming, testing, evaluation (accept any sensible variant of these phases) Each phase is moved down in turn // linear process Phases can be revisited back in turn

Question 50

Spiral model

Answer 50

Incremental design Includes planning, design, programming and evaluation At the end of all 4 phases it repeats Each phase usually adds a new element to the problem Is used to manage risk Prioritises riskiest elements first