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A-Level Computer Science > 1.2 Software > Flashcards

1.2 Software Flashcards

1
Q

What does OS stand for?

A

Operating System

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2
Q

What is an OS?

A

A consistent platform for all software to run on, which manages the hardware, software, security and memory resources of a computer

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3
Q

What are examples of personal desktop PC OSs?

A

Microsoft Windows

Linux

MacOS

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4
Q

What are examples of mobile devices OSs?

A

Android

iOS

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5
Q

What are examples of server OSs?

A

Linux

Windows Server

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6
Q

What is layering?

A

When the user doesn’t need to worry about how application software interacts with the hardware, they just ned to know how to interact with the application software

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7
Q

Is an OS an example of layering?

A

Yes

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8
Q

What are three categories of OS functionality?

A

Hardware

User Interface (UI)

Security

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9
Q

What is hardware functionality?

A

Performs functionality to manage processes that need to be executed by the CPU

Deals with storing and retrieving data and using device drivers to communicate with I/O devices

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10
Q

What are some examples of hardware functionality?

A

Processor scheduling

Handling interrupts

Peripheral management

Memory management

Secondary storage management

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11
Q

How does the OS manage processes?

A

Determines order processes are passed to the CPU and amount of time a process will be allowed before switching to another

OS receives processing requests and sends them to the CPU when they need to be executed and tells the CPU when interrupt is received and pause the current process whilst interrupt completed

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12
Q

Why is processor management needed?

A

CPU needs to execute a large number of processes every second which need to be queued and sent to the processor in the correct order

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13
Q

What is an interrupt?

A

Signal sent to the processor to request immediate attention

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14
Q

How does the OS handle interrupts?

A

Determines if the current process should be paused for interrupt to be executed

If it is, OS stores current contents of registers and loads address of first instruction in ISR for interrupt to be dealt with

When interrupt completed, original process loaded and continued

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15
Q

How does the OS manage peripherals?

A

Manages I/O devices

Communicates with input devices using device drivers and sends data to correct part of computer

Takes data in memory or output from CPU and communicates with output devices using device drivers

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16
Q

How does the OS manage memory?

A

Records how memory in a computer is divided (paging/segmentation) to ensure data allocated fairly

Data needs to be loaded from HDD into RAM when in use and removed from RAM when no longer needed

Ensure enough space in memory to store data requried

Keeps track of where data stored

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17
Q

How does the OS manage secondary storage?

A

Ensures enough space to be able to store required data

Keeps track of where data stored so can be retrieved again

Keeps track of free space

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18
Q

What is a UI?

A

Way of the OS allowing the user to communicate with the device

Can take many forms, type depending on device being used and level of experience of user

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19
Q

What are some examples of an UI?

A

Graphical User Interface (GUI)

Natural Language Interface

Command Line (CLI)

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20
Q

What is a GUI?

A

Way of a user interacting with the device using a series of icons and images

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21
Q

Who is a GUI suitable for?

A

Novice users

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22
Q

What is a Natural Language Interface?

A

Where user can interact with a computer using their natural language

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23
Q

What is a CLI?

A

Method of users being able to interact with a computer where they need to know specific commands to perform actions

Quick if the user knows commands

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24
Q

Who is a CLI suitable for?

A

Skilled users as they need to know the specific commands

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25
Q

What is security functionality of an OS?

A

OS supports security of device by ensuring that resources are protected from unauthorised access through use of permissions and passwords

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26
Q

What are some examples of security?

A

Username and password

User access folders

Restricting access to files and folders

Encryption

Read only

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27
Q

What purpose do username and passwords have?

A

Ensures only users with suitable usernames and passwords can log into a device

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28
Q

What purpose do user access levels have?

A

Manages actions a user can perform depending on their user access levels

Determines if they can see folders, change settings, install software

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29
Q

How is access restricted to files and folders?

A

Password allocated to them, which means the contents are only viewable if the user knows the password

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30
Q

What purpose does encryption have?

A

Data on hard drive encrypted so if someone gained unauthorised access they wouldn’t be able to understand data stolen

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31
Q

What does setting files/folders to ‘read only’ read?

A

So user can view, but not edit, files

Enforced via password of user access levels

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32
Q

How does the OS manage network protocols?

A

Manages network transmission of data and protocols used within, including TCP/IP, HTTP(S), FTP

Establishes connection with device data is being sent to and agrees protocols with device

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33
Q

How does the OS load and run programs?

A
  1. Locate where program is stored
  2. Check if enough space in RAM
  3. Move required data from secondary storage to RAM
  4. Send interface to monitor
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34
Q

What are paging and segmentation?

A

2 techniques enabling OS to make optimum use of memory by splitting the memory into small sections and saving data in non-contiguous data locations

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35
Q

What are memory management operations?

A

Tracking status of memory allocation

Determining storage requirements

Controlling memory usage

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36
Q

How does the OS track the status of memory allocation?

A

Memory divided into physical address spaces

OS initially marks each space as free but, when required, OS loads data into spaces and marks them as allocated

When data or instructions are no longer needed, OS marks spaces as free again allowing data to be overwritten

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37
Q

How does the OS determine storage requirements?

A

Rare that data needed for a process can fit in a single memory locations

Determines how much memory to allocate to each process that’s running, based on requirements of its programming

Reserves blocks of addresses for each process to use

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38
Q

How does the OS control memory usage?

A

Manages swapping between processes and their memory space to provide memory access as required

Main memory is hardware resources with physical addresses used to locate areas in which data and instructions can be stored

When program executed, logical addresses produced and total of these logical addresses makes up logical address space of that process

Maps logical address space to physical address space and memory usage between processes

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39
Q

What is paging?

A

Data split up physically into equal size pages, not considering data it’s storing

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40
Q

What is segmentation?

A

Data split up logically into different size segments, considering data it’s storing

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41
Q

What is virtual memory?

A

Part of the hard drive which is allocated as an extension of RAM

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42
Q

How does the OS manage virtual memory?

A

Swaps data between virtual memory and RAM as required

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43
Q

What factors affect the division of processing time?

A

When task was requested

Importance of task

Length of task

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44
Q

What happens as a computer runs more processes?

A

Longer it takes for a process to be allocated processor time

Unsuitable for processes that must perform tasks almost immediately

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45
Q

What are the reasons a processor can be interrupted?

A

Hardware device has signalled it has data to process

Hardware device has completed a task it was asked to do

Software processor needs a service to be provided or OS function to be performed

Allotted amount of time expired and an action needs to be performed

Hardware failure occurred and needs to be addressed

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46
Q

What does ISR stand for?

A

Interrupt Service Routine

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47
Q

What is an ISR?

A

Mini program that’s been designed to respond to an interrupt’s request

Can be built into an OS or provided via device driver

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48
Q

What are the stages of an interrupt?

A
  1. Processor receives the interrupt
  2. Processor completes the FDE cycle of instruction that was running when it received interrupt
  3. Current contents to processor registers (including PC) saved to memory
  4. Origin of interrupt identified so that appropriate ISR called
  5. All other lower-priority interrupts put on hold to allow ISR to finish running
  6. PC updated with address of first instruction of ISR
  7. ISR completes its execution
  8. Processor registers reloaded with values saved to memory
  9. Lower-priority interrupts that were put on hold re-established
  10. PC set to point to address of next instruction that needs to executed in program that the processor was running when it received interrupt
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49
Q

Rank types of interrupt from highest to lowest

A
  1. Hardware commands
  2. Program/software
  3. Timer
  4. Input/output devices
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50
Q

What are hardware commands/interrupts?

A

Shutdown to start triggered by user pressing off button

Memory parity error (data loaded contains different value than when it was stored)

Internal clock triggers suspending proces

Reset button pressed

Power supply failure

Power-down command (screen off, hibernate)

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51
Q

How does hardware interrupts/commands work?

A

Send a physical signal to the CPU via the interrupt chip

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52
Q

What is a program/software interrupt?

A

Software detects an error has occurred and issues software interrupt for CPU to run some instructions to try and clear error

Illegal instruction encountered an interpreted code

Arithmetic overflow (result of calculation exceeds available storage)

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53
Q

What is a timer interrupt?

A

Data-logger has to read an input sensor every one second

Screen-recording application that has to read next screen update

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54
Q

What are I/O device interrupts?

A

Devices like the keyboard and mouse demand attention or inputs would never get a look in

Hard disk

Optical disk

Printer

Graphics tablet

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55
Q

What are scheduling algorithms?

A

For computer to switch tasks, OS must control suspension of process currently running and control subsequent continuation of another process

Current process suspended and saved into memory and then when CPU is ready to service it, state reloaded and process continued

Scheduling algorithms determines order OS will execute processes

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56
Q

What does a scheduler do?

A

Makes sure time allocated fairly to all processes

Maximises use of CPU and all hardware

Makes applications run as quickly as possible

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57
Q

What are examples of scheduling algorithms?

A

First Come First Served (FCFS)

Shortest Job First (SJF)

Shortest Remaining Time (SRT)

Multi-Level Feedback Queue (MLFQ)

Round Robin (RR)

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58
Q

What is starvation?

A

When a process cannot complete its execution because its constantly denied processor time

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59
Q

What is First Come, First Served?

A

First job to enter ready queue is the first in the running queue

Execute each process in its entirety?

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60
Q

Is FCFS pre-emptive?

A

No

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61
Q

What are the advantages of FCFS?

A

Simplest method to implement

Once a job starts, will definitely be completed

Should avoid starvation

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62
Q

What system does a FCFS work well in?

A

One that only has a few concurrent processes

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63
Q

What are the disadvantages of FCFS?

A

Can be a long wait before a process can run

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64
Q

What is Shortest Job First?

A

Process with the shortest/smallest running time is run next

When a process starts to be executed, it’s executed in its entirety

Jobs sorted in the ready queue according to estimated processor time needed

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65
Q

Is SJF pre-emptive?

A

No

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66
Q

What are the advantages of SJF?

A

Reduces wait times because shorter processes are removed quickly, meaning that the processor can allocate more jobs to longer times

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67
Q

What are the disadvantages of SJF?

A

Time estimation of a job could be wrong and this is what is used to determine which job first

Susceptible to starvation as if shorter jobs keep being added, scheduler will keep prioritising these jobs so longer processes won’t be serviced

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68
Q

What is Shortest Remaining Time?

A

Processor continuously reorders queue during run time

If a process added to the queue has a shorter amount of remaining time, interrupt is raised

Current process suspended in favour of the new one

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69
Q

Is SRT pre-emptive?

A

Yes

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70
Q

What are the advantages of SRT?

A

Short processes executed immediately which is useful for higher performance systems running many small concurrent processes

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71
Q

What are the disadvantages of SRT?

A

Starvation of long-running processes

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72
Q

What is the Multi-Level Feedback Queue?

A

Processor queue split into multiple queues with different priorities

Processor will execute all processes in highest priority queue first then move down the groups

If a process isn’t getting enough CPU time, will be moved to a higher priority queue

If a process is getting an unfair amount of CPU time, will be moved to a lower priority queue

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73
Q

Is MLFQ pre-emptive?

A

Yes

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74
Q

What are the advantages of MLFQ?

A

Eliminates starvation

Can manually flag processes as higher priority to guarantee execution

Processes can be executed very efficiently

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75
Q

What are the disadvantages of MLFQ?

A

More difficult to implement

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76
Q

What is Round Robin?

A

Each process is given a maximum length of processor time in the running state after which it’s put back into the ready queue

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77
Q

What are the time period allocated to the processes called?

A

Time slices

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78
Q

Is RR pre-emptive?

A

No

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79
Q

What are the advantages of RR?

A

Ensures every task is allocated processor time without a long wait

Eliminates starvation

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80
Q

What are the disadvantages of RR?

A

Doesn’t scale well as more processes run, the time slices get smaller

Urgent tasks less likely to be completed quickly

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81
Q

What are the different types of OS?

A

Distributed

Multi-task

Multi user

Embedded

Real time

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82
Q

What is a distributed OS?

A

Processing appears to be completed on a single computer

However, task split and processed on multiple devices acting as a single computer

Data shared between devices

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83
Q

What is an example of a distributed OS?

A

Creating weather satellite imagery

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84
Q

What is a multi-user OS?

A

Enables computer to perform multiple operations at once, or at least, what appears to be

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85
Q

What is an example of a multi-task OS?

A

Someone working on a home computer

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86
Q

What is a multi user OS?

A

Allows multiple users that are on different computers to access single system’s OS resources simultaneously

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87
Q

What is an example of a multi user OS?

A

School system

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88
Q

What is an embedded OS?

A

Found inside other devices

Has a dedicated function

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89
Q

What is an example of a embedded OS?

A

Washing machine / Satnav

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90
Q

What is a real time OS?

A

Ensures tasks are completed within an agreed period of time

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91
Q

What is an example of a real time OS?

A

Hospital

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92
Q

What does BIOS stand for?

A

Basic Input/Output System

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93
Q

Where is BIOS stored?

A

Non-volatile memory

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94
Q

When is BIOS available?

A

When the computer starts

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95
Q

What are the jobs of the BIOS?

A

Initialises and tests hardware in a computer system so it’s ready for use by other software on the computer (POST)

Loads bootloader program (bootstrap) from secondary storage

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96
Q

What does POST stand for?

A

Post-On Self-Test

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97
Q

What does the bootstrap do?

A

Starts initialisation of OS

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98
Q

What would happen without the BIOS?

A

Nothing could be loaded as main memory doesn’t contain any instructions that could start boot process

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99
Q

When do modern systems use BIOS?

A

Only use it during initial stages of booting up a computer because software design’s become so effective that there’s no need for separate programs to be involved, making process more efficient and easier to control

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100
Q

Where is BIOS stored now?

A

Used to be stored on non-volatile ROM chip

Now stored on flash memory systems because more convenient and easier to update software in-place

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101
Q

What does CMOS stand for?

A

Complementary Metal-Oxide Semiconductor

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102
Q

What is a CMOS memory circuit?

A

Has it’s own battery so it can maintain it’s data between restarts

Any configurable settings are stored on CMOS memory circuit

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103
Q

What is CMOS memory circuit used in?

A

Modern computer systems to keep track of key functions

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104
Q

What are the stages when a computer is booted up?

A
  1. Power turned on
  2. Only data from ROM can be used at this point
  3. POST is run, checks all parts that it needs to “come to life” are there and available
  4. Clears anything that may still be in the registers or the CPU
  5. Loads address of the first instruction in the boot program into the PC
  6. Control now passed to boot program that carries out its own checks on the hardware
  7. Checks for any BIOS on the hard disk or on a storage device called CMOS RAM
  8. Combines this with the basic BIOS stored on the ROM and then sent to RAM
  9. This file of information called the boot file
  10. Computer now ready to load OS
  11. OS normally found on hard disk but it will look at other locations first such as additional bootable device if told to do so by BIOS
  12. OS now takes control of the computer and the memory and will load jobs into memory for processing as per the scheduler
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105
Q

What are device drivers?

A

Small programs that are used to control a piece of hardware, providing an interface between OS and hardware

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106
Q

Where would you find device drivers?

A

When you install a new peripheral have to install drivers

May be on CD ROM, downloaded from internet or preloaded in OS

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107
Q

How do the OS and device drivers work together?

A

When OS receives a command (to print) passes this to device driver for that piece of hardware as the device driver knows how to communicate with this piece of hardware

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108
Q

What are the specific device driver functions called?

A

Routines

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109
Q

What is a virtual machine?

A

A host system running software that allows other software to behave as if it were running on a hardware system

Can be configured to replicate any combination of hardware so that software running on it acts as if it were accessing certain devices even if they don’t exist

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110
Q

What is virtualisation?

A

Many VMs running on a single host PC

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111
Q

What are some examples of roles of VMs?

A

Running alternative OSs

Supporting incompatible software

Creating a test system

Running multiple servers

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112
Q

How does a VM run alternative OSs?

A

Created to allow installation of one OS within another OS

Legacy OS or OS that wouldn’t normally be able to run on hardware host

VM can emulate different hardware setups so software runs as if running on different hardware platform

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113
Q

How does a VM support incompatible software?

A

Some older software might not run on newer systems

VM could emulate older system on which user can run older software

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114
Q

How does a VM create a test system?

A

VMs are closed, controlled environments

“Hardware” of VM only exists as self-contained software process that’s isolated from actual host system

Provides opportunity to run software that’s potentially damaging (malware, early versions of software that needs to be analysed)

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115
Q

How does a VM run multiple servers?

A

Servers on network are required to fulfil multiple roles

More than one server can run on a VM, allowing for separation of services without need for multiple pieces of hardware

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116
Q

What are some examples of VMs?

A

Emulators - allow for another system to be used on a PC

Windows VM - used to “make” a PC a MAC

Test environment - enables testing of a game on different systems

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117
Q

What is intermediate/byte code?

A

For all different programming languages, different version needs to compiled for each of the different machines it can be run on

Different languages partially compiled from source code into intermediate/byte code then run on VMs on same PC

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118
Q

What are the three types of software?

A

Operating System software

Utility software

Application software

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119
Q

What is OS software?

A

Manages hardware, software and memory resources of the computer

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120
Q

What are some examples of system (OS) software?

A

OS

Linux

iOS

macOS

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121
Q

What is application software?

A

Enables the user to perform tasks

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122
Q

What are some examples of application software?

A

Word processing software

Graphical editing software

Video editing software

Music production software

Spreadsheet software

Presentation software

Web development software

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123
Q

What is utility software?

A

Maintains, protects and improves performance of the computer

Analyses, diagnoses problems with and tries to fix parts of your system

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124
Q

How does utility software come?

A

Pre-installed as part of OS

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125
Q

What are some examples of system (utility) software?

A

Defragmentation

Decryption

Compression

Anti-virus

Anti-spyware

System info and diagnosis

Firewall

Disk formatting

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126
Q

What is compression software?

A

Used to both compress and decompress files on a computer

Decreases the amount of data inside of files

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127
Q

What are the reasons to compress files?

A

Increasing amount of available space on a secondary storage device (if each file takes up less space, have more available space, good for files used infrequently)

Sending files on a network (if file size smaller, less processing and less time required)

When sending a file with an email (restriction of file size that can be sent, ensures maximum file size isn’t reached)

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128
Q

What is defragmentation?

A

Recognises files on a hard drive

Groups together files so that related data is stored together

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129
Q

Why is defragging necessary?

A

When data is saved on a hard drive, may be split up if first available space doesn’t have enough memory to store all required data

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130
Q

How are files defragged?

A

Moves files to temporary empty space on the HDD

Groups together empty spaces on the HDD

Groups together related files

Replaces data on the HDD so all related data stored together

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131
Q

What is encryption?

A

Process of using an algorithm to convert plaintext into ciphertext

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132
Q

What is the utility software of encryption responsible for?

A

Applying encryption algorithms

Decrypting data using encryption key

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133
Q

When is encryption used?

A

Transferring data securely across a network to prevent it being read in case of interception

On files on a secondary storage device to prevent access to files in case of hacking or theft

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134
Q

What is malware?

A

Malicious software that’s been created with intention to cause damage to a computer

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135
Q

What can malware do?

A

Corrupt files

Delete files

Change files

Steal files

Cause disruption to service

136
Q

What are different forms of malware?

A

Virus

Worm

Trojan

Remote Access Trojan (RAT)

Spyware

Ransomware

137
Q

What is a virus?

A

Malicious form of self-replicating software that attaches itself to other programs or files so that it can make copies of itself and spread easily to infect computer system

Remains dormant in the host file or program until the program is run and it’s able to execute

138
Q

What can a virus be designed to do?

A

Send spam

Steal data

Infect other computers on the network

Corrupt files

139
Q

How can a virus arrive?

A

Via email attachment

Visiting a malicious website

On a removeable storage device

140
Q

Why can viruses be hard to detect?

A

They hide themselves in their host’s file

141
Q

What are worms?

A

Replicate and cause damage to system

Don’t require a host program to spread, they can replicate and distribute independently

142
Q

How can worms spread?

A

Using network features

Email service

143
Q

What are worms typically designed to do?

A

Spread quickly and infect as many devices as possible in order to waste system resources

Use up network bandwidth and slow down network significantly

Sometimes use up all system resources causing a DoS attack

144
Q

What is a trojan?

A

Piece of software that appears to be legitimate to trick user into executing it but also performs malicious actions

Aren’t self-replicating and don’t infect other files

Only operate if the victim runs the program

145
Q

What is the main defence against trojans?

A

Educate users about the risk of downloading and installing software

146
Q

What is usually the main objective of trojans?

A

Steal confidential information

Inflict damage

147
Q

What is a RAT?

A

Computer may become part of a bot under the remote control of a hacker

148
Q

What is a botnet?

A

Network of computers that are under the control of a single operator who can instruct all of the computer to do something at the same time

149
Q

What can a botnet do?

A

Send out spam emails

Perform a distribute denial-of-service (DDoS) attack on a chosen target

150
Q

What is spyware?

A

Type of malicious software that is installed on a device without the user’s knowledge, which captures data from the device and sends it back to the creator

Gathers information on a person and how they use a computer

151
Q

What data can spyware gather?

A

Monitor internet usage

Send harmless but annoying adverts

Taking and reporting back screenshots

152
Q

How can spyware be installed?

A

Visiting a suspicious website

Clicking a link in an email

Downloading a legitimate program that’s been bundled with malware

153
Q

How can spyware be removed?

A

With a removal tool but user must be alerted to its presence in order to know to run the clean-up tool

Routinely run anti-malware tools

154
Q

What is ransomware?

A

Locks a computer or encrypts files and therefore prevents user from accessing their data

Attacker will demand fee is paid before they release the files, although there is no guarantee that the user will get their files back even after they’ve paid the moment

155
Q

What is anti-malware

A

Designed to protect a computer system by detecting and blocking threats

Continually monitors files and software being accessed by OS to detect signs of malicious intent

Software can be configured to deal with different threats

156
Q

What is back up?

A

A copy of the original data is taken and stored in a different location

157
Q

What is archive?

A

Original data is removed and stored in a different location

158
Q

What are the reasons to restore files from backup?

A

Accidentally deleted

Virus infects files

Lose the original

Hardware failure (after fire/flood)

Data changed without intent

159
Q

What are the two types of backup?

A

Full backup

Incremental backup

160
Q

What is a full backup?

A

Backs up everything on the system

161
Q

What is an incremental back up?

A

Only updates files that are changed?

162
Q

What is a disk formatter?

A

Prepares a secondary storage device to be used to store files

Erases any data currently on the device

Makes sure the settings are correct so that it’s compatible with the OS

163
Q

What is a file repair?

A

Designed specifically to recover files that have been corrupted or damaged files that can’t be opened any more

Attempts to repair damage to the file so it can be opened correctly by appropriate software application

Greater range of tools to restore and repair corrupt files

164
Q

What is a disk checker?

A

Scans secondary storage device to check for corrupted files

Attempts to fix errors and gives option to delete them if not possible to restore the files

165
Q

When does a file repair need to be used?

A

When data in file has gone missing or become disorganised making it unreadable by software attempting to open it

166
Q

How can a file be damaged?

A

Bug in the software that wrote data to file

Malware that corrupts file maliciously

167
Q

What is a file manager?

A

Provides GUI to enable user to manage files on their computer (rename, copy, paste, delete)

168
Q

What is a disk repair?

A

Hard disk drive can develop faults that result in sectors becoming corrupted or unreadable

Software repairs disk by replacing data in bad sections with an empty sector so data can be read by computer

169
Q

How can the bad sectors be caused?

A

Sudden loss of power

System crashes

Disk being exposed to static electricity

170
Q

What can bad sectors cause?

A

Computer to run slowly

Files to become inaccessible

Whole disk to become unreadable

171
Q

What is open source software?

A

Source code can be read and edited

Comes in a readable format

Can be tailored to needs to developer

172
Q

What are some examples of open source software?

A

Linux

Libre Office

Firefox

VirtualBox

VLC

173
Q

What are the advantages of open source software?

A

Can share software with others

User can modify it

Source code available for all to see

Free licence

New versions must come with same sharing/freedom licences

174
Q

What are the disadvantages of open source software?

A

Support must be paid for

Finished quality of software can vary, although some can be very high quality

175
Q

What is closed source software?

A

Source code cannot be read, edited or adapted

Applications come as executable format

Usually licence fee charged

Developed by commercial company

176
Q

What are some examples of closed source software?

A

Adobe

Google Earth

Microsoft Office

177
Q

What are the advantages of closed source software?

A

Support is usually free, although a premium can sometimes be charged

Developer provides free updates for a set length of time

Company obliged to provide software that’s fit for purpose as covered by Trades Description Act

178
Q

What are the disadvantages of closed source software?

A

Source code not readily available

Software cannot be altered

Software cannot be shared with others

179
Q

What are open source applications?

A

Code available for other parties to see and alter

180
Q

Who pays the development cost of open source applications?

A

Spreads cost of development

Often volunteers will improve the code for free

181
Q

Is code available in open source applications?

A

Available for other parties to see and alter

182
Q

Who are open source applications often developed by?

A

People who do not have full knowledge of all the functionalities and methods used by the software, so solutions may be inefficient

183
Q

Are there deadlines for open source applications?

A

No deadlines for development

Software often has ‘quick fixes’ to solve problems rather than full solutions to problems so there is no guarantee that the software will function fully

184
Q

How are open source applications tested?

A

Lack formal development methods and testing which can make the software unreliable

185
Q

Who pays the cost of development of closed source applications?

A

Wholly funded by the company

Costs recovered through sales

186
Q

Is code available in closed source applications?

A

Kept by author

Only executable distributed

187
Q

Who are closed source applications often developed by?

A

Professionally developed in-house by the company that produced the program

Technical solution is fully understood and improvement will be able to incorporate this to produce a more efficient solution

188
Q

Are there deadlines for closed source applications?

A

Has formal deadlines and timescales for updates and produced with full solutions which the company is accountable for

189
Q

How are closed source applications tested?

A

As developed in-house, tested fully and not released until software considered reliable

190
Q

What is machine code?

A

List of binary instructions in memory that the CPU fetches one line at a time and decodes what they mean before executing them

191
Q

What is an opcode?

A

First binary value

Operation code

192
Q

What is an operand?

A

Second binary value

Address in memory of the data to be processed

193
Q

What is assembly language?

A

Replaced opcode with mnemonic (one-to-one relationship)

Needs a translator to convert code to machine code

194
Q

What are the problems with machine code?

A

Error-prone

Takes a long time to write

Lots of repetitions

Inefficient code

195
Q

What is an instruction set?

A

Complete list of instructions supported by processor

196
Q

What is source code?

A

Programs originally written in high or low level languages

197
Q

Can source code be run by a computer?

A

Not unless it’s translated

198
Q

What are high-level languages?

A

Consist of key words and command statements

199
Q

What are the advantages of high level languages?

A

Understandable - commands easier to learn, write and debug

Portable - can be transferred and used on different types of computer (translator not source code that handles computer’s architecture)

Problem-focused - focus attention on problem-solving, not dealing with hardware specifics for machine it’s run on

200
Q

What are the three types of translator?

A

Assembler

Interpreter

Compiler

201
Q

What language is an assembler suitable for?

202
Q

What is an assembler?

A

One mnemonic in assembly language equivalent to an opcode

Different assembler needed for each machine or chipset

203
Q

What language is an interpreter most useful for?

A

High level

204
Q

How does an interpreter work?

A

Code is put onto user’s machine along with interpreter

Translated line by line

Next line only translated if line before has no syntax errors

Once a line translated, code executed by CPU

If there is an error, program won’t run and user will be shown error

205
Q

With an interpreter, can source code be viewed?

206
Q

What are the advantages of interpreters?

A

Don’t need to recompile software and distribute to different platforms when changing software

Can change code and will be interpreted by relevant interpreter on hardware (compatibility across platforms)

207
Q

What are the disadvantages of interpreters?

A

Have to have correct interpreter to run on a different computer

Can be slower to run as being translated one line at a time

208
Q

What code is a compiler most suitable for?

A

High level

209
Q

How does a compiler work?

A

Translates code written in a high level language to object code

Checks all lines of code for syntax rules then converts entire source code into object coed

Code fully translated into object code and executable file made

Executable file can run on user’s machine but differs depending on the type of machine being used

210
Q

With a compiler, can source code be viewed?

211
Q

What are the advantages of compilers?

A

Source code cannot be seen when running the file as it is already translated

Quick to run as already translated

212
Q

What are the disadvantages of compilers?

A

Can take long time to translate as all done at once

May find a lot of errors as translating all code at once

213
Q

What is intermediate code?

A

When compiler/interpreter only translates code to ‘half-way’ stage (more efficient)

Provides ‘standard form’ of code for translation to machine code

High-level -> intermediate -> machine

Can be run on a VM allowing code to run faster than interpreted code while allowing code to run cross-platform unlike compiled code

214
Q

What does stages of compilation mean?

A

Set of stages that source code goes through so that executable object code can be produced

215
Q

What are parses?

A

To translate code from source to machine code, translator run through series of parses

Each parse of code designed to carry out certain tasks

216
Q

What should there be at the end of the parses?

A

Efficient machine code that can be ru

217
Q

What are the stages of compilation?

A

Lexical analysis

Syntax and semantic analysis

Code generation and optimisation

218
Q

What are the tasks in lexical analysis?

A

Removes all white space and comments

Turns remaining code into tokens

Creating a symbol table

219
Q

What is removed in lexical analysis from the code?

A

Comments

Spaces

Blank lines

220
Q

How does lexical analysis turn the remaining code into tokens?

A

Compiler looks for operators, reserved words, variables which are split into tokens

Analyses each line of code and assigns token to each part of the code

Identifiers checked against set of rules

Reserved words (print) only used as keyword tokens

221
Q

What does a symbol table store?

A

Identifier or key word

Token class

Data type

Run time address or value

Scope

222
Q

What are some examples of token classes?

A

Integers

White space

Identifiers

Keywords

Operator

Individual token classes

223
Q

What simple error-checking occurs in lexical analysis?

A

Look for illegal identifiers

x and y would be flagged

Misspelt keywords and undeclared variables NOT detected

224
Q

Does syntax or semantic analysis come first?

225
Q

What is syntax analysis?

A

Code is checked against rules of the language

226
Q

What happens in syntax analysis?

A

Analysis syntax of the statements to ensure they conform to the rules of grammar for the computer language in question

Abstract Syntax Tree created

227
Q

What are some examples of syntax rules?

A

Indentation

Missing brackets

Keywords misspelt

Missing code

Undeclared variables

228
Q

What is an Abstract Syntax Tree?

A

Maps structure of program, first dropping the brackets, semicolons, etc that were used by the programmer

If required tokens missing from the tree or in the wrong place, compiler will report an error

229
Q

What does an AST help identify?

A

Errors in the structure of the code

230
Q

What is semantic analysis?

A

Code is checked to see if it is valid within the given context

231
Q

What are some examples of semantic errors?

A

Data type declaration mismatch

Trying to access an array index that is out of bounds

Variables being used before they’ve been declared

Wrong number of parameters passed into subroutine

Trying to access a variable that’s out of scope

Attempting to use a reserved word from the language (e.g. print) as a variable name

232
Q

What happens in code generation and optimisation?

A

Separate program is created that is distinct from the original source code

Code generated is object code (binary equivalent of the source code)

233
Q

What is object code?

A

Executable version of the code BEFORE LINKED LIBRARIES ARE INCLUDED

234
Q

What happens in code generation?

A

AST converted into object code

Major distinguishing feature between compilation and interpretation is interpreters don’t produce a separate executable file

235
Q

What is code optimisation?

A

Takes place throughout the process but mainly in the final stage

Attempts to reduce execution time of compiled program

Removes redundant code and makes code as efficient as possible

Reduces amount of memory as some variables may not be required and speeds up the processing as it’s more efficient

236
Q

What are the advantages of code optimisation?

A

Some compilers will be better at optimisation that others (what can make a good compiler)

More efficient code

Less memory needed

Quicker processing of code

237
Q

What are the disadvantages of code optimisation?

A

Some optimisation may remove code it thinks is redundant and may give unexpected results

Can take a long time to optimise code

238
Q

What is a library?

A

A pre-written collection of code that allows the programmers to import functionality into their own programs

239
Q

What are programming libraries?

A

Gives you access to many specialised functions

Saves programmers from having to reinvent the wheel when writing a new program

Usually been thoroughly tested and is therefore reliable and efficient

240
Q

What are some examples of programming libraries?

A

random - makes random choices

tkinter - creating GUI

pygame - creating Python game

matplotlib - creating graphs

numpy - performing mathematical operations on arrays

pandas - analysing, cleaning, exploring and manipulating data

241
Q

What are linkers?

A

Used to combine together compiled code from various sources along with any code being pulled in from pre-written libraries into a single executable program file

242
Q

What do linkers do?

A

Resolve all cross-references between the object code files created through compilation and creates a single executable program

Includes any links to any library code required by the object code into an executable file

243
Q

What are the two types of linking?

A

Static

Dynamic

244
Q

What is static linking?

A

Code needed from the libraries is copied and included in the executable file

245
Q

What are the advantages of static linking?

A

Code doesn’t need to access external libraries during run time

Therefore if a library is missing on the client computer, the program will crash

246
Q

What are the disadvantages of static linking?

A

However compilation could take a long time

Executable will be large and take up more space in RAM

247
Q

What is dynamic linking?

A

Compiled versions of the libraries are stored on the computer and linked with the code by the OS at run time

248
Q

What are the advantages of dynamic linking?

A

Less memory needed therefore quicker to process

Less code needed to compile so it is quicker

249
Q

What are the disadvantages of dynamic linking?

A

If a library is missing, the code will not run

250
Q

What is a loader?

A

A program which is part of the OS which is responsible for loading the correct files and libraries into the main memory when the program is run (used when dynamically fired)

251
Q

What does SDLC stand for?

A

Systems Development Life Cycle

252
Q

What are the stages of a SDLC?

A

Analysis

Design

Development

Testing

Evaluation

Maintenance

253
Q

What happens in the analysis stage of a SDLC?

A

Feasibility study (cost, timescale, possibility)

Research (interviews, observation, data flow, future plans/growth of company)

Processing and defining user requirements so they’re understood

Finding out existing problems software is trying to solve

Working out what data will be in the system and its origin, uses, volumes and characteristics

What needs to be done in systems and what happens if error occurs

254
Q

What are the outputs of the analysis stage of SDLC?

A

Problem definition - clear explanation of problem and its domain

System requirements/objectives - clear description of what the systems need to do (specific, measurable, achievable, realistic, time bound)

255
Q

What happens in the design stage of an SDLC?

A

System architects oversee design process where they draw attention to specific skills and expertise from UI designers, database designers

Database

Hardware and software required

Test plan

Design specification - document

256
Q

What are the outputs of the design stage of a SDLC?

A

UI (design menus and UIs)

System outputs (reports, emails, graphs)

Algorithms (flowcharts, pseudocode, modular structure)

What data structures data will be held in

Security features

257
Q

What happens in the development phase of a SDLC?

A

Code solution

Most projects completed in teams with wide range of experience and skills so can specialise in their area of expertise when working

If done by organisation, will be set style and standards that follows company’s in-house conventions

Project manager oversee project through development process

White box testing where each module is tested as it is developed by examining code written and efficiency and alpha testing

258
Q

What happens in the testing phase of a SDLC?

A

Testing for robustness and whether it fulfils the criteria

Black box testing where inputs and outputs of systems are examined

Beta testing

259
Q

What happens in the evaluation phase of a SDLC?

A

Can be carried out throughout the project but mainly done once project completed

Reviewed in terms of functionality, effectiveness, usability, reliability, maintainability, extendibility

Compared against requirements

Technical documentation - explains how system works and allows for those taking over code in future to understand work done

User documentation - required for more complex parts of the code and for those less experienced

Client signoff

260
Q

What happens in the maintenance phase of a SDLC?

A

Agreed maintenance period

Fixing bugs that arise in the system

Changing software where it doesn’t work

261
Q

What is scope creep?

A

Additional requirements added during the project

262
Q

What are the software development methodologies?

A

Waterfall

Spiral

Rapid application development (agile methodology)

Extreme programming (agile methodology)

263
Q

What is the waterfall method?

A

Each stage is completed in turn so stages and COMPLETED SEQUENTIALLY

Next stage doesn’t start until previous one is completed, signed off and documented

Previous stage can be returned to however developers must then complete next stages

CLEARLY DEFINED stages

264
Q

When is the client involved in a waterfall method?

A

Analysis stage to help project team work out requirements of system

Then little involvement until project is developed

265
Q

What are the suitable uses of a waterfall method?

A

When requirements are very clear and well-defined (at beginning of project)

Large-scale development projects due to ease of management

Not suitable for innovative or complex projects

266
Q

What are the advantages of the waterfall method?

A

Everyone is very clear on their responsibilities at each stage

Simplicity makes it easy to manage

Easy to see if project is running to schedule

267
Q

What type of method is the spiral model?

A

Iterative method

268
Q

What is the spiral model?

A

Always complete a RISK ANALYSIS in a cycle (whether cost is spiralling, timeframe, out of data technology, changing business processes)

In each cycle, prototype is developed, reviewed and evaluated

269
Q

When is the client involved in the spiral model?

A

Review with client in EVERY CYCLE to get client feedback

270
Q

What are the suitable uses of the spiral model?

A

Large, complex projects where risk is a key factor

Projects containing high level of risk or uncertainty

Large scale problems

271
Q

What are the advantages of the spiral model?

A

Risk placed at the heart of this model

Excellent for projects which contain high level of risk or uncertainty

Very suitable for large scale problems

272
Q

What are the disadvantages of the spiral model?

A

Risk is SUBJECTIVE (what one person sees as a big risk, may not be considered such a big risk to a project)

Need to have a member of the team skilled in identifying and quantifying risk, which is highly specialised skill

Takes time in the project and costs money

Complex nature of risk analysis adds to expensive

If risk analysis done badly, project will suffer

273
Q

Which methodologies are classified as agile methodologies?

A

Rapid Application Development (RAD)

Extreme programming

274
Q

What are agile methodologies?

A

Prototypes are created and feedback gained from the client ASAP

Feedback used to inform next prototype

275
Q

What are the suitable uses of agile methodologies?

A

Small to medium projects

276
Q

What are the advantages of agile methodologies?

A

Can be used for big projects if decomposed into sub-projects

277
Q

What are the disadvantages of agile methodologies?

A

Can result in scope creep

278
Q

What is RAD?

A

Based on building a SERIES OF PROTOTYPES each of which adds to the previous and is reviewed by the client

Less emphasis on planning and documentation and more on developing something and then using this to inform next stage

Objectives/requirements GRADUALLY REFINED during each stage/prototype

279
Q

What are suitable uses of RAD?

A

When client requirements not well defined

Not suitable for projects where code efficiency is important (focus on usability rather than how product works)

Doesn’t scale well for large projects with big teams

280
Q

What are the advantages of RAD?

A

Initial prototypes developed quickly

Requirements don’t need to be entirely clear from the start

Continuous feedback from client means end project likely to have excellent usability

281
Q

What are the disadvantages of RAD?

A

Poorly written, inefficient, patched code

Regular contact must be maintained at all times

282
Q

What is extreme programming?

A

Series of short releases and short cycles

Each release is fully working

Focus on refinement/quality and efficiency of code (completed through PAIRED PROGRAMMING)

Development/feedback loops shorter as prototypes not produced but FULLY WORKING versions produced

283
Q

When is the client involved in extreme programming?

A

Continual interaction as member of client team part of development team

284
Q

What are the advantages of extreme programming?

A

Efficient, robust code produced

Fewer bugs on release and high performing software

Has a very high emphasis on programming so quality of end code likely to be very high

285
Q

What are the disadvantages of extreme programming?

A

Difficult if not all of team and end user can be in same place

Client must be able to commit to having a full time representative working with development team

Requires team of programmers working in close collaboration, unlikely to work well if distributed geographically

286
Q

What are the types of testing?

A

Black box testing

White box testing

Beta testing

Alpha testing

287
Q

What is black box testing?

A

Tests just inputs and outputs

Not concerned with quality of algorithms

288
Q

What is white box testing?

A

Tests logic of a problem

All paths through

Quality of algorithm checked

289
Q

What is alpha testing?

A

Tests very early version of software

Restricted to company

Employees provide feedback

290
Q

What is beta testing?

A

Tests almost finished version of software

Extended

Invited group of external testers who provide feedback

291
Q

What is the order of the four types of testing?

A

Start of development

  • white box testing
  • black box testing
  • alpha testing
  • beta testing

End of development

292
Q

What are programming paradigms?

A

Used to specify an overall approach to writing program code

293
Q

What is Turing complete?

A

Most programming languages in most paradigms are this

Can solve all problems a computer is able to solve

294
Q

What is the structure of programming paradigms?

A

Types of languages -> low level, higher level

Low level -> machine language, assembly language

Higher level -> imperative, declarative

Imperative -> procedural, object-orientated

295
Q

What is imperative language?

A

Write a sequence of instructions for the computer to perform using sequence, selection and iteration

Focus is on stating HOW A COMPUTER SHOULD OPERATE (TELLING IT WHAT TO DO)

296
Q

What is a declarative language?

A

Focus on what the program should achieve, the OUTCOMES OF THE CODE

Used in intelligent systems and makes use of a knowledge base

297
Q

What is an example of a declarative language?

298
Q

What is a procedural programming paradigm?

A

Where program code is divided up into self-contained procedures/functions (subroutines) which are discrete blocks of code that carry out a single task

Systems built by combining these procedures

Procedures share data by passing data between them or through global variables

Procedures have their own variables not accessible from outside the procedure

299
Q

What is the programmer responsible for in a procedural paradigm?

A

Specifies steps needed to execute the programmer and in what order

300
Q

How is logic of a program expressed in a procedural programming paradigm?

A

Series of procedure calls

301
Q

What are some examples of procedural languages?

A

Pascal

C

Visual Basic

Python

302
Q

What is an object-orientated paradigm?

A

Identify the self-contained objects that make up the system and the way they interact with each other

Systems built around objects

Each object contains both program routines (methods) and data being processed

Objects can be easily reused and inherited without having to rewrite code

Because objects are self-contained and simple they are more reliable and easier to program

303
Q

What is the programmer responsible for in an object-orientated paradigm?

A

Designed self-contained objects

304
Q

What are some examples of object-orientated languages?

A

C++

Delphi

Java

Visual Basic

305
Q

What are the characteristics of assembly language?

A

One-to-one relationship with machine code

Use mnemonics (short codes) to represent specific sets of machine code 1s and 0s

Specific to processor

Use symbolic address as labels to reference locations of data in memory

306
Q

What are low-level languages?

A

Specific to instruction set of the processor

Defined by processor manufacturer

Makes code written non-portable (only run on processor of same type it was written for)

307
Q

What are some examples of LMC instruction set?

A

LDA - load

STA - store

ADD - add

SUB - substract

INP - input

OUT - output

HLT - end program

BRZ - branch if 0

BRA - branch always

BRP - branch if 0 or positive

308
Q

What modes of addressing is used in high level languages?

A

Mode of addressing is abstracted from the developer

309
Q

What mode of addressing is used in assembly language?

A

Developer would directly use different modes of addressing depending on what they wanted to do

310
Q

What are the different modes of addressing?

A

Immediate

Direct

Indirect

Indexed

311
Q

What is immediate addressing?

A

Hard coding the value into the instruction

Operand is not a memory address but the value to be used

312
Q

How fast is immediate addressing?

A

Fastest method as don’t need to access computer’s memory

313
Q

What is direct addressing?

A

Operand is absolute memory address is used and not the value

Relies on value always correctly being at the location specified, which may cause problems if the code is moved

314
Q

When is direct addressing generally used?

A

For a computer system that uses only one program that wouldn’t be relocated in memory (on an embedded system)

315
Q

How fast is direct addressing?

A

Quick method but not as quick as immediate

316
Q

What is indirect addressing?

A

Often used with linkers and loaders

Address of data held in an intermediate location - therefore address of where the data is stored must be looked up

Point to a memory location that contains physical address of where we need to get data from

Data (such as programming library) can be put in memory location and therefore be moved

Address of where to find this stored as intermediate address

Intermediate address location part of instruction

317
Q

How fast is indirect addressing?

A

Slower than previous methods but more flexible when loading larger amounts of data

318
Q

What is indexed addressing?

A

Final address of data determined by starting address and an offset

Use an index to offset the value and find the appropriate value within an array

319
Q

What is indexed addressing used for?

320
Q

What is a class?

A

A template outlining attributes (properties) and methods (actions/behaviours)

321
Q

What are instantiated from classes?

322
Q

What is an object?

A

Instance of a class

323
Q

What is an attribute?

A

A piece of data to store about an object/a property of an object

324
Q

What is a method?

A

The action that can be performed on an object

325
Q

How are methods created?

A

Adding subroutines to a class definition

326
Q

What is encapsulation?

A

Implemented by setting attributes and methods to public/private

Object should bind together attributes and methods that manipulate the data

Does this so that data is protected

327
Q

What is public vs private?

A

Attributes and methods can be set to these to determine if code external to the class can call/access the attributes/methods or not

Getter and setter methods are used to access attributes that cannot be directly accessed by code external to the class

328
Q

What is polymorphism?

A

A method can perform different actions depending on the object it is called on

329
Q

How is polymorphism implemented?

A

By overriding where an inherited method is redefined in a subclass and therefore this would override the inherited method when called

330
Q

What is over-loading polymorphism?

A

Implementing a method multiple times to accept different parameters

331
Q

What is overriding polymorphism?

A

Implementing an inherited method differently in a sub/child class

332
Q

What is inheritance?

A

Where ALL ATTRIBUTES AND METHODS from a parent/super class can be used/called within a child/sub class

333
Q

What is multiple inheritance?

A

When a class has two or more parent classes

334
Q

What is a constructor?

A

Called when an object is created/instantiated

335
Q

What is a constructor used for?

A

Initialising attributes

336
Q

What is a constructor in Python?

A

__init__()

A-Level Computer Science (8 decks)

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