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computer science ocr a level > 1.2.2 applications generation > Flashcards

1.2.2 applications generation Flashcards

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1
Q

What are the two main types of software?

A
  • System Software
  • Application Software
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2
Q

why are both system and application software needed

A
  • Systems software controls hardware, provides platform for applications software, manages memory + provides a user interface
  • Applications software will allow tasks to be performed
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3
Q

What is system software?

A
  • OS and utility software
  • also code translators, Library Program
  • Software designed to run computer’s hardware + applications, managing its resources (memory, processors + devices)
  • also provides platform for running application software.
  • system software is typically bundled with a computer’s OS
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4
Q

Library Programs (System Software)

A
  • contains useful functions that are frequently used by programs.
  • Simplifies the process of application development.
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5
Q

what is utility software

A
  • software that performs specific task relating to upkeep of system
  • designed to keep computer safe + running efficiently as well as provide useful tools to manage files and apps.
  • sits alongside OS
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6
Q

what comes under utility software

A
  • antivirus / anti-malware
  • defragmenter
  • backup
  • compression
  • firewall
  • file repair
  • device drivers
  • file management
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7
Q

what useful analogy can be made about utility software

A
  • think of utility software like MOT
  • car = OS. if you don’t maintain it, it loses performance
  • so with computers, OS allows it to run. But without utility software to protect with firewalls and anti-virus, create backups and run defragmentation, it can lose performance
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8
Q

What is application software?

A
  • Word processor, web browser, video editor, games, social networking, text and vice communication, graphics manipulation, spreadsheets, database etc.
  • A program which provides an interactive service to the user + allows them to perform a task.
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9
Q

factors to consider when choosing applications (5)

A
  • functionality
  • hardware
  • availability
  • cost
  • reliability
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10
Q

what is a generic application and give example

A
  • application that doesn’t have specific/narrow purpose as you can use it to carry out different tasks and meet multiple needs
  • word processor / presentation tools
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11
Q

what is a specific application and give example

A
  • highly specific and bespoke software. specific application software only installed on systems with direct need for it.
  • database software (beyond creating, managing and using database, it has little use)

(although you can duplicate functionality within more generic app like spreadsheet software, it may not suit needs)

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12
Q

for this scenario, recommend application software company may need:

  • an independent games development company that makes apps for mobile phones and tablets
A
  • word processor (produce progress reports, capture bug reports, notes at design meetings for new projects)
  • graphics manipulation (produce assets for game)
  • software development tools (write, test and debug code)
  • communication software (email team members, contact potential clients / distributors)
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13
Q

what is hardware

A
  • physical parts of a computer system and its related devices both internal or external
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14
Q

what is software

A
  • general term covering all programs that run on a computer system
  • falls into broad categories like application, system and utility
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15
Q

What is off the shelf software?

A
  • Software that is available to be purchased from a company as a full working package.
  • tends to be general application software
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16
Q

list disadvantages of bespoke software (custom written)

(benefits of off the shelf software)

A
  • you have to wait for the product to be made
  • will cost a large amount of money to produce
  • has not been ‘tried and tested’
  • there are likely off the shelf alternatives
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17
Q

What does an antivirus / anti-malware do?

A
  • helps to keep computer + files safe by detecting and removing malicious programs which have been designed to harm a computer.

examples of malware (viruses, trojans, spyware, worms)

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18
Q

What does a disk defragmenter do?

A
  • reorganises files on hard disk, putting fragments of files and free space together so that files are stored contiguously in disk memory
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19
Q

what does defragmentation reduce the movement of and why is this beneficial

A
  • reduces movement of read/write head across disk surface –> speeds up file access
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20
Q

What do compression utilities do?

A
  • Reduces size of a file so it takes up less space and so can download faster over the internet
  • data is either lost (reduces quality of image/audio file) or represented in different way using binary (retains original data in new compressed format)
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21
Q

What does a file manager do?

A
  • manages/organises data storage. Allows files, directories and folders to be accessed, created, moved, copied, renamed and deleted.
    – Manage the storage of software
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22
Q

what is file repair?
and what is a file repair facility often built into?

A
  • files can become corrupt / damaged
  • file repair software attempts to rectify these issues and restore file to original working state
  • a file repair facility is often built into certain apps as well as being a separate, dedicated software tool found in most OS’s or from independent vendors
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23
Q

What do backup utilities do?

A
  • Provides way to make a copy of data/files and store them on different storage medium so that if original is lost / corrupted in some way, it can be retrieved.
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24
Q

how does backup software often come

A
  • bundled with OS but can also be purchased by separate vendor
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25
Q
  1. what 3 ways can backups be set up
  2. what are the 2 types of backups
A
  1. set up to be manual, automatic or scheduled
  2. full and incremental backups
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26
Q

what is the purpose of the utility software: hardware drivers

A

– Purpose: Enable peripheral and OS to communicate
– Uses: To configure hardware e.g. used to install a new keyboard, mouse or printer

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27
Q

What is proprietary / closed source software?

A
  • software which is designed by a company and is supplied pre-compiled.
  • source code isn’t available so cant be modified (protected by Copyright Designs and Patents Act)
  • e.g. Microsoft word
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28
Q

Give pros of closed source software.

A
  • Lots of documented support (support by developers who don’t release source code)
  • More likely to be free of bugs
  • Companies have a lot of resources providing security
  • more polished user friendly product
  • creators have financial gain
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29
Q

Give drawbacks of closed source software.

A
  • Software cannot be altered to make it more suitable for a specific user’s needs
  • Software costs money (required to have license per user or computer)
  • You have to wait for the company to update the software to fix bugs
  • demand from community for developments (creators)
  • piracy issues (creators)
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30
Q

What is open source software?

A
  • Software that is free for anyone to download + edit as its supplied with source code.
  • installed on any number of computers
  • can be developed by a community (support provided by community) and tweaked to suit an individual user’s needs.
  • e.g. Linux
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31
Q

Give pros of open source software.

A
  • FREE!
  • community modification (code modified = more suitable for a specific user’s needs)
  • You do not have to pay for newer versions
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32
Q

Give drawbacks of open source software.

A
  • Lack of documented support
  • creators = little-to-no financial gain
  • Can be less user-friendly to use
  • Potential security issues with downloading code which could be edited by anyone
  • Quality of code can vary –-> more prone to bugs
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33
Q

What is general purpose software?

A
  • Off the shelf software which contains many features that will satisfy every potential users needs.
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34
Q

Give benefits of general purpose software.

A
  • Well tested
  • Relatively cheap
  • Lots of documentation
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35
Q

Give a drawback of general purpose software.

A
  • Large file size as it contains so many features
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36
Q

What is special purpose software?

A
  • Can be off the shelf (such as SIMS for schools) or bespoke.
  • Software that is designed only for specific users but not average user.
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37
Q

What is bespoke software?

A
  • Software that is designed by a company exclusively for a user/organisation so that it can fulfill their exact needs.
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38
Q

Give a benefit of bespoke software.

A
  • guaranteed to fulfill the exact needs of the user.
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39
Q

Give a drawback of bespoke software.

A
  • expensive and time consuming to develop.
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40
Q

Give a benefit of off the shelf special purpose software.

A
  • available immediately and is cheaper than bespoke.
41
Q

Give a drawback of off the shelf special purpose software.

A
  • may not fulfill the exact need of the user and may contain many extra features, increasing file size.
42
Q

what is translation

A
  • process of converting source code to machine code
  • done by interpretation or compilation
43
Q

what is source code

A
  • descriptive and easy for us to understand, read, maintain and debug.
  • can be easily translated into machine code so that it can be processed by the CPU.
44
Q

What is a translator?

A
  • piece of software which translates code from one language to another, usually from a high level language (source code) to machine code since CPU can only understand binary machine code to be bale to process it.
45
Q

What are High-level languages

A
  • e.g. Visual Basic, C++, and Python
  • used to write programs that are independent of computer architecture they will run on.
46
Q

To move from high-level source code to executable machine code source code is required to be what

A
  • high-level source code –> executable machine code requires source code to be translated.
47
Q

What are the three main types of translator?

A
  • Compiler
  • Interpreter
  • Assembler
48
Q

what is an assembler?

A
  • converts low level assembly language (basic commands and operations) directly into machine-executable code (1 to 1 relationship) that can be recognised by a specific type of processor
49
Q

advantages of an assembler / assembly language

A
  • mnemonics easier to remember for when coding in assembly language
  • memory-efficient
  • speed of execution is faster
  • hardware orientated
  • requires fewer instructions to accomplish same result
50
Q

disadvantages of an assembler / assembly language

A

-long programs written is assembly language cant be executed on small computer
- takes lots of time to code program as it’s more complex in nature
- lack of portability between computers of different makes

51
Q

what is machine code

A
  • code that the processor understands
  • made of a opcode and operand
52
Q

what is Machine-executable code

A
  • Machine-executable code is processor dependent meaning that same source code has to be translated into different object codes for processors that use different instruction sets.
53
Q

what is byte code

A
  • Byte code is the intermediate code, partially translated by an interpreter so it can be compiled and executed by a VM (interpreted by a VM)
54
Q

why is bytecode being partially translated advantageous

A
  • partially translated to improve portability between different hardware
55
Q

fill the gaps:

same ________ can be created from different _____________ meaning same ____________ can be used to run bytecode regardless of o________ c_____ l____________

A
  • bytecode
  • languages
  • translator
  • original coding language
56
Q

what does translator check before deciding how to translate bytecode and why?

A
  • translator checks hardware before deciding how to translate so it can be executed on that computers hardware
57
Q

why does bytecode run slower than fully translated code

A
  • it still needs further translation
58
Q

what is object code and what does it require the use of to produce executable code?

A
  • Code that has been translated into machine code, without its required library code.
  • object code requires the use of linkers
59
Q

what is executable code

A
  • Fully translated code, ready to be processed by a CPU. (combination of object code and library code)
60
Q

What does an interpreter do?

A
  • translates one line of source code at a time into machine code as program running
  • each line executes before translating next line
61
Q

Give an advantage of interpreters

A
  • easier to debug code as the program runs up to the line where the error is. also allows beginners to try commands as it will pause if its an error
  • code doesn’t need to be recompiled when changed
  • beneficial for developers in testing stage (errors identified on line they occur)
62
Q

disadvantages of interpreters

A
  • translation software required at run-time. user must have the interpreter installed
  • slower speed of execution (one line translated at a time)
  • code is not optimised
  • source code is required
63
Q

Give some examples of interpreted languages.

A

Python, JavaScript, Ruby

64
Q

What does a compiler do?

A
  • Translates entirety of source code into object code and then machine (executable) code to be processed by CPU
65
Q

Give an advantage of compilers.

A
  • When program has successfully compiled, the executable file will not need to be translated again
  • useful if you wish to create standalone executable file to enable it to be run on multiple platforms
  • faster execution times, as no further translation required (no need for translation at run time)
  • code usually optimised
  • high level language source code easier to write
66
Q

Give a disadvantage of compilers.

A
  • can be difficult to find bugs in compiled code as it is compiled all at once. (less effective at highlighting syntax errors)
  • wont run until error free
  • code needs to be recompiled when changed
  • designed for specific type of processor
67
Q

Give some examples of compiled languages.

A
  • C++
68
Q

compiling process stages. what are they?

A
  • Lexical Analysis
  • Syntax Analysis
  • semantic analysis
  • Code Generation & Optimisation
69
Q

What is compilation

A
  • Compilation is the translation process that produces executable object code from source code through stages including lexical and syntax analysis, code generation and linking library routines.
70
Q

what has to have happened before stages of compilation occur

A
  • source code must be created
71
Q

what is the purpose of each parse in order to get further from source code and closer to machine code

A
  • each parse is designed to carry out set of tasks and prepare code for next stage of compilation
72
Q

what is lexical analysis

A
  • comments and white spaces used to improve readability + indent code are removed by compiler as they aren’t necessary for executable code (this happens as a result of lexer)
  • lexer converts lexemes in source code into series of tokens –> each element is tokenised meaning its purpose is identified
  • each token added to a symbol table used by compiler to keep track of all of the elements identified in the program.
73
Q

name some different token classes

A
  • identifier (function or variable name)
  • keyword (if, else, function, return)
  • separator ()
  • operator (+ * / %)
  • literal (hello world)
  • number (0,6,8)
  • quote (“ “)
  • bool (True False)
  • datatype (int, str)
74
Q

what are lexemes

A

individual items broken into tokens e.g user_name or =

75
Q

what is syntax analysis

A
  • Once tokens assigned to the code elements, compiler checks that the tokens are in correct order + conform to rules of programming language used.
  • All programs have to be written in accordance to languages rules otherwise translator would be unable to translate code.
  • compiler analyses the syntactical structure of input checking that code has valid syntax + it produces a list of any syntax errors found.
  • Syntax analysis will produce an abstract syntax tree (AST) to represent program which will enable it to trace through the opcodes and operands, processing code in the correct order.
76
Q

what is an Abstract syntax tree (AST)

A
  • created during syntax analysis stage
  • maps structure of program dropping brackets, semicolons, etc. that were used by programmer.
  • Every language produces a different AST depending on its syntax.
77
Q

If required tokens missing from AST or in wrong place, what does compiler do

A
  • If required tokens missing from AST or in wrong place, the compiler will report an error.
78
Q

what is the purpose of an AST

A
  • map program’s structure which will enable it to trace through the opcodes and operands to process code in correct order.
79
Q

what is Semantic analysis

A
  • semantic analysis is used to flag/highlight logic errors
80
Q

what is Code generation

A
  • Following prior stages, separate program is created that is distinct from original source code.
  • The code that is generated = object code
  • During this stage, compiler converts AST into object code meaning all source code is translated into object code
81
Q

what stage of compilation provides the major distinguishing feature between compilation and interpretation and why.

A
  • Code generation = major distinguishing feature between compilation and interpretation since interpreters don’t produce a separate executable file.
82
Q

what is Code optimisation

A
  • The optimiser identifies redundant (lines that have no impact on program) or repeated code + remove or rearrange code as necessary
  • This ensures it runs efficiently + faster so that it minimises the amount of memory it requires to run.
83
Q

when can code optimisation happen and what does it depend on

A
  • Optimisation can happen during or after code generation, depending on the compiler.
84
Q

what do High-level languages come with pre-written and where relevant precompiled?

A
  • libraries.
85
Q

what are Libraries

A
  • pre written, ready-compiled and tested collections of code that allows programmers to import functionality into their own programs (give you access to specialist functions)
86
Q

give example of library in python

A
  • math library (.factorial, .pi, .trunc, .remainder, .sqrt etc)
87
Q

How are libraries used to compile code?

A
  • code to perform complex tasks already written, compiled + packaged as a library
  • so, compiler can simply access this instead of recompiling
88
Q

What are the advantages of using libraries?

A
  • save time, code is not rewritten
  • pre-compiled so are optimised to run quickly
  • Library code from reliable source has usually been thoroughly tested –> efficient + reliable.
  • quick + easy to use. programmers aren’t required to have expertise to use
89
Q

What are the disadvantages of using libraries?

A
  • adding functionality or making specific tweaks can be difficult / impossible
  • you can become “black-boxed” (function usually hidden from / mysterious to user) from actual implementation
  • you have to trust developers will continue to maintain library + tested it completely
90
Q

someone programming in windows OS can call what library. And to do what?

A
  • Dynamic Link Libraries
  • contains sub-routines written to carry out common task on windows OS like “save as”
91
Q

what is a linker

A
  • software tool used to combine compiled code with necessary library code during compilation, resulting in a single executable file (executable code)
  • linker resolves all of the cross-references between the several object code files and creates a single executable file.
92
Q

why are linkers required

A
  • a programmer may have made use of libraries so linker is required to link library code to object code to produce executable code which can be processed by CPU.
93
Q

what are static linkers

A
  • link + load the various library code to program’s main code to produce program’s executable file during compilation
  • results in large executable program file but all the code needed to run the program is always present.
94
Q

what are dynamic linkers

A
  • OS links up library code when it is required at runtime (it will not be compiled together with program)
  • results in smaller size of compiled machine code
  • but if dynamic library changes or required linker is not present on host computer when certain library code is required, program cannot run.
95
Q

for dynamic linking, where are compiled versions of required libraries stored?

A
  • compiled versions of required libraries stored on host computer
96
Q

what are Loaders

A
  • Part of OS that is responsible for loading executable program file into memory (copies executable code into RAM) as part of execution stage, ready to be run.
97
Q

if using dynamic linking, what must loaders also be responsible of doing

A
  • loaders will be responsible for loading required libraries into memory
98
Q

which application emulates the use of loaders and in what way

A
  • process of loading can be emulated by the LMC
  • assembly code in left-hand pane is loaded into available memory locations by loader.
  • Once program halted, the memory locations are freed for use by other programs

computer science ocr a level (15 decks)

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