1.2.2 Applications Generation

Question 1

What are the two main categories of software?

Answer 1

• Applications Software
• Systems Software

Question 2

Applications Software

Answer 2

Designed to be used by the end-user to perform one specific task.

Types:
- Off-the-shelf
- Proprietary
- Open Source
- Custom Written

Examples:
- Desktop publishing
- Word processor
- Spreadsheets
- Web browsers

Question 3

Systems Software

Answer 3

Needed by the system to control hardware and run applications.

Types:
- Utility Software
- Translators
- Library Programs
- Operating Systems

Question 4

Utility Programs

Answer 4

Optimise the performance of a computer and perform useful background tasks

Examples:
- Disk defragmenter
- Automatic backup
- Automatic updating
- Antivirus software
- Compression software

Question 5

Disk Defragmentation

Answer 5

• Re-arranges the contents of the hard drive so they can be accessed faster to improve performance
• Will try to ensure all parts of a file are contiguous by moving other parts as necessary
• File allocation table (FAT) may be used to show file placement

Recommended to have 15+% of space left when defragging so the file can be copied and moved (in case of corruption)

Question 6

Defragmentation Benefits

Answer 6

• Files are stored closer together
• Resulting in a faster access time

Question 7

Automatic Backup

Answer 7

Backup of data in permanent storage can be automated, specifying:
- Where (Backup location)
- When (Backup time)
- What (What data is backed up)
- How (Backups compressed or not)

Question 8

Automatic Updating

Answer 8

Runs in background, detecting software update releases and automatically installing them

Some updates may add new software features, or fix security issues

Question 9

Antivirus Software

Answer 9

Scans permanent storage for viruses by comparing files to known virus definitions

• Must be kept up to date with new virus definitions to be effective
• May sometimes flag a harmless file as a virus

Question 10

Compression Software

Answer 10

Can reduce the size of files - useful for sending files across the internet

Question 11

Application Software Types

Answer 11

• General Purpose
• Bespoke
• Special Purpose

Question 12

General Purpose Software

Answer 12

Can be used by the general public

(e.g. General apps, spreadsheets, calculator)

Question 13

Bespoke Software

Answer 13

Software custom created for a specific user/company

Question 14

Special Purpose

Answer 14

Software used by a small fraction of the public

(e.g. Graphic design apps, accounting apps)

Question 15

Open Source Software

Answer 15

Allows anyone to access its source code

• Anyone can modify and sell it, on the condition that the software produced is open source too

Question 16

Benefits of Open Source Software

Answer 16

• Can be modified and improved by anyone
• Technical support from online community
• Can be modified and sold

Question 17

Disadvantages of Open Source Software

Answer 17

• Support available online may be insufficient or incorrect
• No user manual
• Lower security as it may not be developed in a controlled environment

Question 18

Closed Source Software

Answer 18

Software that doesn’t allow the public access to the source code

-Provided as a fully compiled, executable set of files
- Users usually have to pay for access to the software -> they are buying a license to use the software, NOT the software itself
- May be restrictions on how the software is used after purchase

Question 19

Benefits of Closed Source Software

Answer 19

• Thorough, regular and well-tested updates
• Company that owns the software can provide expert support or create a user manual
• High levels of security due to it being professionally developed

Question 20

Disadvantages of Closed Source Software

Answer 20

• License can restrict how many people can use the software at once
• Users cannot modify and improve the software

Question 21

Application Selection Criteria

Answer 21

• Functionality - Does it do what you want it to do?
• Hardware - Will it run on the hardware?
• Availability - Already exists or already written?
• Cost - How much is it?
• Reliability - Are there bugs, has it been tested?

Question 22

Types of Translators

Answer 22

• Compilers
• Assemblers
• Interpreters

Question 23

Compilers

Answer 23

Translates the entire program from high level language to machine code

• Produces hardware-specific executable files written in machine code (called object code) that can be downloaded

Question 24

Interpreters

Answer 24

Translates high level language into machine code going line by line

Question 25

Benefits of Compilers

Answer 25

- Program can be run many times without needing to recompile - Faster to execute - Executable code doesn't require the interpreter to run - Compiled code cannot be easily read & copied by others

Question 26

Benefits of Interpreters

Answer 26

- Source code can be run on any machine with the interpreter - If a small error is found, the entire program doesn't need to recompile - Useful for debugging as it can return the location of the error

Question 27

Assemblers

Answer 27

Translates assembly code instructions to machine code Each processor has its own instruction set so the object code will be hardware specific

Question 28

Stages of Compilation

Answer 28

- Lexical Analysis - Syntax Analysis - Code Generation - Code Optimisation

Question 29

Lexical Analysis

Answer 29

- All unnecessary comments and spaces removed - Keywords, constants & identifiers replaces with tokens corresponding their function in the program - Information about the token associated with each keyword or identifier is stored in a symbol table that the lexer creates

Question 30

Syntax Analysis

Answer 30

- Stream of tokens from previous stage split up into tokens - Each phrase is checked against the rules of language to make sure they're valid - If the phrase is not valid, an error will be recorded - Semantic analysis also carried out, in which logic mistakes within the program are detected - Abstract Syntax Tree produced (a representation of the source code in the form of a tree)

Question 31

Code generation

Answer 31

The abstract syntax tree produced in the previous stage is used to produce machine code (A major distinguishing feature between compilers and interpreters - compilers produce an executable file while interpreters don't)

Question 32

Code Optimisation

Answer 32

Aims to: - Remove redundant instructions - Replace inefficient code with code that achieves the same result but in a more efficient way Risks: - This stage can significantly add to the overall time taken for compilation - Excessive optimisation may alter the way in which the program behaves

Question 33

Library

Answer 33

Pre-compiled programs which can be incorporated within other programs (via linkers) Library functions can be called within a program

Question 34

Use of Libraries

Answer 34

Used to provide a specialised range of functions which would otherwise require a lot of time and effort to develop - Ready-to-use - Error free - Save time developing & testing modules - Can be reused within multiple programs

Question 35

Linkers

Answer 35

Piece of software that is responsible for linking external modules and libraries included within the code

Question 36

Types of Linkers

Answer 36

- Static - Dynamic

Question 37

Static Linkers

Answer 37

Adds modules and libraries directly to the main file. - Increases the size of the file - Updates to the modules and libraries externally won't affect the program, meaning a specific version of a library can be used

Question 38

Dynamic Linkers

Answer 38

Includes addresses of modules and libraries in the file where they are referenced Loader retrieves the program at the specified address for execution when the main program is run _Pro_: - File remains small and external updates feed through to the main file