OCR AS Computing - Software

OCR AS Computing - Software

1. Application Software

   • General Purpose
     • Word processor
     • Spreadsheet manager
     • Graphics packages
     • Media editors
     • Used for many different purposes
   • Special Purpose
     • Off-The-Shelf
       • Less expensive since cost is shared to all other people buying the package
       • May contain a lot of unwanted features
       • Ready to be installed immediately
       • Well-documented, tested and error free
     • Bespoke
       • More costly and requires expertise in analysing document requirements
       • Features are specific to the customer's needs
       • May take a long time to develop
       • May contain errors which may not be immediately apparent
     • Used for a single specific task

2. Systems Software

   • Operating Systems
   • Utility Programs
     • Disk Defragmentation
     • Automatic Backup
     • Automatic Updating
     • Virus Checker
     • Compression Softwaree
   • Library Programs
   • Translators

3. Open Source

   • Software is licensed for use but anyone can use it
   • Software is distributed with access to the source code so anyone can modify it
   • Developers can sell the software
   • New software created from the original software must also be open source

4. Closed Source

   • Restrictions on how the software is used (e.g. limited to one user)
   • The creator of the software holds the copyright - the user only has a license to use it
   • No access to the source code
   • Lots of support is available from the creator
   • Regular updates and support lines are available

5. Programming Language Translators

   • Assembler
     • Low-level language
     • Each instruction in assembly code almost always equivalent to one machine code instruction
     • The instruction set of a computer are completely dependent on its hardware
     • Before assembly code can be executed, it must be translated into machine code
       • The assembler does this.
         • Takes each assembly code instruction and converts it into 1s and 0s of the corresponding machine code
         • Input: source code
         • Output: machine code
   • Interpreter
     • Looks at and analyses each line of a program
       • Translates into machine code
         • As long as there's no syntax errors
           • Advantages Over Compilers
             • Platform independence - source code can be run on any machine with appropriate interpreter
             • Useful for program development as no need for lengthy recompilation after each error discovered
     • May run slower than a compiled program as each statement has to be translated to machine code every time it is encountered
   • Compiler
     • Translates high level language into machine code
     • Input: source code
       • Output: machine code
     • Scans through source code several times
       • Each scan performs a different check and builds information to produce the final object code
         • Different hardware platforms require different compilers as object code is hardware specific
     • Advantages Over Interpreters
       • Object code can be saved on disk and run whenever required
       • Object code is executed faster than interpreted code
       • Object code can be distributed or executed without having the compiler present
       • Object code is more secure, can't be read easily
     • Appropriate for a program that is run frequently with little change and if the program is being distributed to places without access to the source code