1.5 Application Generation

Question 1

Application Software

Answer 1

• Software designed to be used by the end-user to perform one specific task
• Requires utility software to run
• E.g Word processing, spreadsheets, web browser

Question 2

Systems Software

Answer 2

• Low-level software responsible for running the computer smoothly, interacting with hardware & providing a platform for applications to run
• Ensures high performance for the user
• E.g: File Management, Anti Virus, OS, device drivers

Question 3

Utilities

Answer 3

• Each utility program has a specific function linked to the maintenance of the operating system
• Compression: Enable files to compressed/decompressed. Used when
  sending large files over Internet
• Disk defragmentation: Rearranges the contents of the hard drive so they
  can be accessed faster, improving performance.
• Antivirus: Detects potential threats to the computer, alerting user & removing threats.
• Automatic updating: Ensures the OS is kept up to date, updates automatically installed when the computer is restarted. Ensures the system is less vulnerable to malware/hacking threats.
• Backup: Automatically creates routine copies of specific files selected by the user. Files can be recovered in the event of a power failure, malicious attack etc.

Question 4

Open Source Software

Answer 4

• Used by anyone without a license & is distributed with the source code
• Adv: Can be modified/improved, wide support, can be sold on
• Disadv: Support may be poor, lower security

Question 5

Closed Source Software

Answer 5

• Requires user to hold appropriate
  license to use it. Cannot access the source code due to copyright license
• Adv: Regular & tested updates, expert support, high security
• Disadv: License limits use, cannot modify

Question 6

Translators

Answer 6

• Program that converts high-level source code into low-level object code, then ready to be executed by a computer
• 3 types of translator (Compiler, Interpreter, Assembler)

Question 7

Compiler

Answer 7

• Translates high-level code into machine code all at once, after carrying out checks & reporting back any errors
• This initial compilation process is longer than using an interpreter or an assembler. If changes need to be made, the whole program must be recompiled
• The machine code produced can only be executed on certain devices - compiled code is specific to a particular processor type & OS
• Code can be run without a translator being present

Question 8

Interpreter

Answer 8

• Translate & execute code line-by-line
• Stop and produce error if line contains an error
• Slower than running compiled code as code must be translated each time it is executed with an interpreter.
• Useful for testing sections of code & pinpointing errors
• Requires an interpreter in order to run on different devices. However, code
  can be executed on a range of platforms as long as the right interpreter is available, making interpreted code more portable.

Question 9

Assembler

Answer 9

• Assembly Code: Low-level language, next level up from machine code
• Platform specific, as the instructions used are dependent on the instruction set of the processor
• Assemblers translate assembly code into machine code, code is
  translated on almost a one-to-one basis

Question 10

Stages of Compliation

Answer 10

Lexical Analysis: Whitespace & comments are removed from code
- Remaining code analysed for keywords & names of variables & constants. Replaced w/ tokens & information about the token associated with each keyword/identifier is stored in symbol table

Syntax Analysis: Tokens are analysed against the grammar/rules of language
- Any tokens that break the rules are flagged as syntax errors & added to a list
- E.g undeclared variable, incomplete set of brackets
- Abstract syntax tree is produced, represents source code in the form of a tree. Further detail about identifiers is also added to the symbol table
- Semantic analysis also carried out, where logic mistakes are detected.
- E.g multiple declaration, undeclared identifiers

Code Generation: Abstract syntax tree used to produce machine code

Optimisation: Detect & remove insignificant, redundant parts of the code.
- Replace repeated sections with more efficient code without altering behavior.
- Optimise for runtime performance, even if it increases compilation time.
- Excessive optimization might change program behavior

Question 11

Linkers

Answer 11

• Responsible for linking external modules & libraries in the code. 2 types of linker:
  Static: Modules and libraries added directly into machine code
• Increases the size of the file
• Any updates to modules/libraries will not affect the program. So a specific version of a library can be used
  Dynamic: Compiled versions of required libraries are stored on host computer
• When the program is run, OS links required code from library
• Files remain small, external updates, no need to rewrite code
• May change & call wrong routine

Question 12

Loaders

Answer 12

• Programs provided by the operating system
• When a file is executed, the
  loader retrieves the library/subroutine from the given memory location

Question 13

Use of Libraries

Answer 13

• Libraries are pre-compiled programs used via static or dynamic linking.
• Ready-to-use, error-free libraries save time in module development and testing.
• Can be reused across multiple programs.
• Offer specialized functions, saving time & effort in development
• Utilize others’ expertise, avoiding redundancy in programming tasks.
• Popular libraries offer mathematical and graphical functions.