Application Generation

• Hardware is the physical components of a computer
• Software is lines of non-physical instructions that control hardware in order to make it useful
• A type of software is systems software - this maintains and manages the hardware of a computer system to make it run efficiently
• Application software is another type of software - it performs user-driven tasks
• System software has 2 categories:

  • Operating Systems
  • Utilities
• Examples of application software include:

  • Word processor - creates and stores text documents
  • Database - stores maintains and allows access for data
  • Web browser - Retrieves information from other parts of the internet and transfers it to the computer
  • Graphics Manipulation - enhances graphical images
• A generic application is a type of application that does not have a specific purpose. It can carry out multiple types of tasks, including those that are not related to the original purpose of the application.
• An example of a generic application is word processor
• A specific application is highly specific to a certain task

  It only tends to be installed on systems where it has a direct need

  An example is database software
• Word processors can be applied to any scenario - as long as they are justified why
• A utility software is a housekeeping software. It configures, optimizes, maintains and protects a computer system so that it runs as efficiently as possible
• There are some types we need to now:

  • Antivirus
  • Compression software
  • Backup software
  • File managing software
  • Defragmentation software
  • Device Drivers
  • File repair software
• Files can become corrupt or damaged

  As a result, file repair software attempts to correct such issues so as to restore a file to its original working state

  It is often built into applications, or can be independent
• Back-up software can be set to being manual or automatic

  It backs up important files by copying them and placing them in memory

  It can perform full backups or incremental backups

  It may also back-up to an off-site cloud system

  It usually comes part of the OS but can be bought separately
• Compression software reduces the size of a file so that it takes up less space in memory and can be sent and downloaded faster off of the internet

  It first extracts the files before reading

  It can carry out both lossless and lossy compression
• Defragmentation software reorganises the order of files in a hard disk, placing fragments of files and free space back together

  This speeds up the movement of the read/write head across the disk, speeding up file access

  This is only necessary for hardware with moving parts
• Antivirus software is software that is designed to detect and block malware attacks, and can be updated to protect against the latest threats
• Disk cleanup software is software that presents unused or rarely used files to the user, and at their will, deletes them from the hard drive, freeing up space
• Open Source software:

  • Users can distribute and modify the source code
  • Can be installed on any number of computers
  • Support is provided by the community as a whole
  • Users have access to the source code at all times
  • May not be fully tested
• Benefits of open source software:

  • Software is free to use
  • Wide modification means errors can be fixed quicker
• Drawbacks of open source software:

  • Can be poorly supported
  • Some features may not be well tested
  • Little to no financial gain for creator
• Closed source software:

  • Protected legally by the Copyright design and Patents act
  • Users cannot modify the software
  • Usually paid for and licensed per user or per computer
  • Supported by the developers
  • Source code is not released
  • Tested by developers prior to release
• Benefits of closed source software:

  • It tend to be well supported and well built for users
  • Creators can also gain financial profit
• Drawbacks of closed source software:

  • For users, there is a cost or ongoing subscription fee
  • Piracy issues for creator
  • Constant demand from community for creators to make more features and updates
• A CPU can only execute code when it is in machine code

  It cannot directly execute source code in a high level language
• The process of converting source code to machine code is known as translation
• There are 3 types of translators

  • Compiler
  • Interpreter
  • Assembler
• A compiler works by checking the whole code for any errors, and if it is error free, translates into machine code in just one go
• Advantages of compiler:

  • No need for translation at run-time
  • Speed of execution is faster
  • Code is usually optimized
  • Does not reveal source code
• Disadvantages of compiler

  • Program will not run with syntax errors
  • Code needs to be recompiled
  • Designed for a specific type of processor
• An interpreter translates high level code into machine code line by line
• 4 stages of compilation:

  • Lexical analysis
  • Syntax analysis
  • Code generation
  • Code optimisation
• Lexical analysis:

  • Its input is the source code
  • Words in the source code are converted to a series of tokens - a token is a binary string of fixed strength
  • It places each lexeme inside a token class
  • Whitespaces and comments are removed from the code
  • Tokens are then inputted into a symbol table
  • Outputs tokens to prepare code for syntax analysis
• Syntax analysis:

  • This takes the tokens and the symbol table as its input
  • It checks for syntax errors by placing tokens in an abstract syntax tree
  • It breaks where errors are detected and reports to the user
  • The output of this is the parse tree , or the abstract syntax tree
  • The tree strictly follows syntax rules
• Code generation:

  • This takes the parse tree as an input
  • This is where machine code is generated
  • This is the binary instructions in 1s and 0s that are executed by the processor
• Code optimisation:

  • This aims to reduce the execution time of the program
  • It spots redundant instructions
  • Removes subroutines that are never called
  • Removes constants and variables that are never referenced
• Assembler:

  • translates assembly code to machine code
  • Takes basic commands in assembly code and translates to CPU-specific binary
  • one-to-one process
• Advantages of assembler:

  • memory efficient
  • Faster speed of execution due to simple instructions
  • Hardware-oriented
• Libraries are ready-compiled and pre-tested programs that can be run when needed
• Examples of libraries:

  • turtle library
  • random library
  • math libraryu