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Computer Science > 1.2 Software and Software Development > Flashcards

1.2 Software and Software Development Flashcards

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1
Q

What is the need, function and purpose of an operating system?

A

An operating system is the software that manages the computer;

  • manages the hardware of the system
  • manages the interface between the user and the computer
  • manages the programs being run and installed
  • manages the security of the system
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2
Q

What is paging?

A

Where programs are divided physically into equal sized blocks so that it is using memory efficiently

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3
Q

What is segmentation?

A

Programs are divided logically and split into blocks containing modules or routines

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4
Q

What is the role of interrupts?

A

A signal sent to the processor requesting attention for a particular event. When an interrupt is raised, an ISR is run

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5
Q

What is ISR?

A

Interrupt Service Routine
Only carried out if it has higher priority than the current task
Contents of the CPU are transferred to a stack
ISR is loaded by changing the values of the PC to where it starts in memory
When complete the previous task is loaded from memory into the registers

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6
Q

Describe Round Robin

A

Each process is given a fixed amount of time to execute and if it does not finish it is put onto the back of the queue

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7
Q

Describe first come first serve

A

The first process to arrive will be the first to be dealt with and is completed in its entirety

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8
Q

Describe multi-level feedback queues

A

Uses a number of queues which have different priorities

Jobs can move between queues

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9
Q

Describe shortest job first

A

Needs to know which process will take the shortest and will then complete this one first

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10
Q

Describe shortest remaining time

A

Runs the process that has the least amount of time left

If another process arrived which has a shorter time it will switch jobs

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11
Q

Describe and explain the purpose of a distributed os

A

Allows a group of computers to work on a single task. It can control and co-ordinate many computers, presenting them to the end user as though they were a single system

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12
Q

Describe and explain the purpose of an embedded os

A

Specifically designed for the device on which they run and with efficiency in mind. Operate on low-powered CPU’s with little RAM. Will only likely to have one job

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13
Q

Describe and explain the purpose of a multi-tasking os

A

Organises the computer when it is running several applications at once.

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14
Q

Describe and explain the purpose of a multi-user os

A

Allows more than one user to share the computers resources at a time. Common on mainframe systems where there may be many users accessing them simultaneously

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15
Q

Describe and explain the purpose of a real time os

A

Designed to carry out actions in a guaranteed amount of time even when left running for long periods. i.e. hospitals and safety critical systems

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16
Q

Describe the purpose of the BIOS

A

Basic Input Output System - is what allows the computer to start up. Stores the load instructions

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17
Q

Describe the purpose of device drivers

A

A piece of software that is supplied with the device that allows the operating system to communicate with the device

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18
Q

What is the purpose of virtual machines?

A

Runs a simulation of an operating system on top of the current one, so that the user can test a program that may be used on multiple platforms. Often programs may not run on the provided operating system, so a virtual machine may be needed to run the desired program

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19
Q

What is the difference between utility and application software?

A

Application software allows the user to produce something or perform a task whereas utility software is usually a small program concerned with the maintenance of the system

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20
Q

What is the difference between open and closed source software?

A

Open - Software where the source code is publically available, users can modify the software to suit their needs
+ Free
+ Can change code to suit needs
- Coding can be poor
- Subject to viruses as ‘hackers’ can access code before they have a chance to fix issues
Closed - Software that is only distributed as an executable file
+ Works better as developed by companies
+ Reliable and efficient
- Not always what the customer needs

21
Q

What is an interpreter?

A

Converts high level language, translates and executes code line by line
+ can find the errors as they occur and give specific direction
+ same piece of code can work across different platforms
- lower performance
JavaScript uses an interpreter

22
Q

What is a compiler?

A

Converts high level language, translates all the code into object code and then executable code
+ faster to convert
- keeps source code private
- can’t use across different platforms

23
Q

What is an assembler?

A

Converts low level language (assembly code) into machine code

24
Q

State the stages of compilation

A

Lexical Analysis
Syntax/Semantic Analysis
Code Generation
Code Optimisation

25
Q

What is a linker?

A

The job of the linker is to include links to any library code required by the object code and put this into one executable file

26
Q

What is a loader?

A

The loader is responsible for loading the correct files and libraries into the computer memory when the program is run

27
Q

Describe and evaluate the waterfall life cycle

A

Each stage is started after the previous is finished
Can go back a stage
Works well with a clear expected output at each stage
+ Easy to manage
+ Easy to see if project is running to schedule
- Carries a lot of risk
- Not suitable for complex projects
- Client doesn’t see the project until the end
- Misunderstood requirements can lead to a project that is not easy to fix

28
Q

Describe and evaluate agile methodologies

A

Designed to deal with projects with changing requirements

29
Q

Describe and evaluate the purpose of extreme programming

A 
Example of agile methodologies 
Focuses on producing high quality code 
Paired programming 
Client becomes part of the team 
\+ High quality code
- Client must be able to commit 
- Doesn't work if programmers are distributed geographically
30
Q

Describe and evaluate the spiral model

A 
Designed to manage risk
New prototypes made with each cycle 
\+ Risk is considered
\+ Suitable for large scale projects
- Risk analysis makes it expensive
31
Q

Describe and evaluate rapid application development

A

Involves a series of prototypes
Continous client involvement to inform the development
Suitable for projects that don’t have clear requirements from the start
+ Requirements don’t need to be clear
+ Continuous client feedback
- Not suited for projects where code efficiency is important
- Not appropriate for large scale projects
- Regular contact with the client must be maintaned

32
Q

Evaluate high level code

A

+ easier to code
+ more understandable
+ can code more complicated programs
- lose control over the instructions being executed

33
Q

Evaluate low level code

A

+ faster to compile
+ more control over the CPU and the instructions executed
- will only work on the CPU with the instructions referenced

34
Q

Describe lexical analysis

A

Breaks the code down into a series of tokens by; removing white space and comments, remaining code turned into tokens, symbol table is created to keep track of variables and subroutines

35
Q

Describe syntax/semantic analysis

A

If any tokens break the rules of the language, errors are generated at this point
Abstract syntax tree is built from tokens produced in previous stage

36
Q

Describe code generation

A

Object code is the machine code before the final step (the linker) is run. Abstract code tree converted into object code

37
Q

Describe code optimisation

A

Tweaks the code so that it will run as quickly as possible and use as little memory as possible

38
Q

Explain static linking

A

The code needed to form the libraries is copied and included in the executable file. The code doesn’t need to access external libraries during run time, therefore if a library is missing the program will not crash

  • can take a long time
  • large file size, takes up more space in RAM
39
Q

Explain dynamic linking

A

Compiled versions of the libraries are stored in the computer and linked with the object code by the OS at run time
+ less memory is needed therefore quicker to process
+ less code needed to compile
- if a library is missing the program will crash

40
Q

What is a library?

A

Pre-written modules of code for the user to interact with.

41
Q

What is a paradigm?

A

Different forms of programming languages; low level, high level, imperative, procedural, OOP

42
Q

What is imperative programming?

A

Mainly used within assembly code. It is a sequence of instructions where subroutines are not used. The program is directed around the code using GOTO statements and branches

43
Q

What is procedural programming?

A

A sequence of instructions however the code is split into subroutines and the sequence of code is based on these i.e. IF WHILE FOR

44
Q

What is OOP code?

A

For use in large software projects where code needs to be repeated. Way of inheriting and creating classes

45
Q

What are the 4 addressing modes?

A

Immediate
Direct
Indirect
Indexed

46
Q

Describe and evaluate intermediate addressing

A

Addressed from the binary operand value. The operand is not a memory address but the value to be used
+ fastest method as you do not need to access the computers memory

47
Q

Describe and evaluate direct addressing

A

References the address that the data is stored in
+ quick method however not as quick as intermediate
- relies on the value always being correct at the location specified

48
Q

Describe and evaluate indirect addressing

A

References a place in memory which then points to the data

- address of where the data is stored must first be looked up

49
Q

Describe and evaluate indexed addressing

A

Start number then add the address to find the address of where the data is stored
- slower than previous methods but more flexible when loading larger amounts of data
+ good for data structures which require large blocks of data

Computer Science (8 decks)

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