1. 2. 2 Applications Generation Flashcards
1
Q
Nature of applications (Application Vs System Software)
A
- Software categorised as application or system software
- Application software designed to be used by end-user to perform specific task
- Requires systems software to run, Word and Web Browsers examples of Applications
- System software, low-level software, responsible for running computer system smoothly
- Interacts with hardware, provides platform for application software to run
- User does not directly interact with system software
- Ensures high performance for the user, OS and Device drivers’ examples of system software
2
Q
Utilities
A
- Software that performs specific task, usually related to upkeep of the system
- Compression, files compressed and decompressed, easier to transmit over internet
- Disk Defragmentation, when HDD read/write times slow down
- File fragmented (stored different parts of HDD), defrag rearranges HDD, contents accessed faster improved performance
- Antivirus detects potential threats, alerts user to take action (remove threat)
- Automatic update, OS kept up to date, tackles bugs and security flaws, ensure system less vulnerable to malware and hacking threats
- Backup, auto creates routine copies of specific files selected by user, how often also specified by user
- If accident where to occur (power failure), files can be recovered
3
Q
Open Vs Closed Source
A
- Source code is written by programmer, refers to object code before it has been complied
- Open Source (Source code available to public), Closed Source (Source code not available)
- User chooses open or closed depending on suitability of software to task they will be using it for
- User must consider cost (implementation, maintenance, staff, license) and functionality (features, ease of use)
4
Q
Open Source
A
- Used by anyone without a license, distributed with source code
- Can be modified and improved by anyone
- Technical support from online community
- Can be modified and sold on
- Support available online could be insufficient, incorrect, no user manuals
- Lower security, not be developed in controlled environment
5
Q
Closed Source
A
- Requires user to have appropriate license to use it, cannot access source code, company has copyright licence
- Regular and well tested updates
- Expert support from company, user manuals
- High levels of security, developed professionally
- License restricts amount of people that can use software at once
- User cannot modify/improve software themselves
6
Q
Translators
A
- Translator, program that converts high-level source code into low-level object code, ready to be executed by computer
- Types of translators, compiler, interpreter and assembler
7
Q
Compiler
A
- Translates high-level code into machine code at once, after checks done, errors reported
- Initial compilation longer than other translators, if changes need to be made whole program needs to be recompiled
- Code can only be executed on certain devices once it has been compiled into machine code
- Specific to processor type and OS, code can run without presence of translator
8
Q
Interpreter
A
- Translates high-level code into machine code line by line
- Stops and produces an error if error in line
- Slower than running compiled code, must be translated each time it is used with interpreter
- Useful for testing sections of code, pinpointing errors, save time compared to compiling whole program
- Requires an interpreter to run on different devices can be executed on range of platforms with correct interpreter
9
Q
Assembler
A
- Assembly code, low level language, platform specific (instructions used dependent on instruction set of processors)
- An instruction set is the complete set of all instructions in machine code that can be recognised and executed by the CPU
- Assembler translates assembly code into machine code, one line assembly equivalent one line machine code
10
Q
Stages of compilation
A
When compiler used, high level code goes through 4 stages before its turned into object code that is ready to be executed, Lexical Analysis, Syntax Analysis, Code Generation, Optimisation
11
Q
Stages of compilation
A
When compiler used, high level code goes through 4 stages before its turned into object code that is ready to be executed, Lexical Analysis, Syntax Analysis, Code Generation, Optimisation
12
Q
Lexical Analysis
A
- White space and comments are removed
- Remaining code analysed for keywords / names of variables and constants, replaced with tokens
- Information on tokens associated with the keyword or identifier is stored in the symbol table
13
Q
Syntax Analysis
A
- Tokens are analysed against the grammar and rules of the programming language
- Anything that breaks these rules is flagged as a syntax error that is added to a list of errors
- Examples of syntax errors include undeclared variable type or an incomplete set of brackets
- Abstract syntax tree is produced represents the source code in the form of a tree
- Further detail about the identifiers added to symbol table
- Semantic analysis carried out where logic mistakes within the program are detected
- Examples of semantic errors- multiple declarations, undeclared identifiers
14
Q
Code Generation
A
- Abstract syntax tree used to produce machine code
15
Q
Optimisation
A
- Aim is to make code faster to execute
- Can add time to overall time taken for compilation
- Redundant parts of code detected removed
- Repeated sections grouped and replaced with more efficient code that produces the same result
- Optimisation may alter how program behaves
16
Q
Linkers, Loaders and Use of Libraries
A
Linkers and loaders allow us to use external pieces of code (subroutines and libraries) from outside sources.
17
Q
Linkers
A
Software responsible for linking external modules and libraries included within the code.
18
Q
Static Linking
A
- Modules and libraires directly added to main file
- Increase size of file
- Specific versions of library can be used because it is not affected by external updates
19
Q
Dynamic Linking
A
- Addresses of modules and libraires included in file, referenced
- When the program is run, loader retrieves modules and libraires from specified address so it can be executed
- File remains small and external updates feed through to main file (no need to rewrite code)
20
Q
Loaders
A
Programs provided by operating system, when a file is executed, loader retrieves library of subroutine from given memory location.
21
Q
Libraries
A
- Pre-compiled programs which can be incorporated in other programs using static or dynamic linking.
- Ready to use and error free
- No need for developing and testing modules therefore time saving
- Can be reused for multiple programs
- Provide specialised range of functions which would otherwise require time and effort to develop
- Saves programmers from “reinventing the wheel”
- Examples of libraries include mathematical and graphical functions
