software

software

1. levels of computer language

   • high
     • A high level language is a programming language that allows code to be written which is similar to a natural human language, such as English.
       • Some programmers prefer to use high level programming languages as they are easier to understand, learn and program as commands are more English-like and identifiers can be long and meaningful.
       • High level programming languages also allow the use of powerful commands that perform quite complex tasks such as MsgBox in Visual Basic or the SORT clause in COBOL.
   • low
     • Low level programming languages do not resemble natural languages, such as English or Welsh. They are made up entirely of bit patterns (instructions or data) that can be executed directly by the CPU.
       • Low level language are useful when speed of execution is critical or when writing software which interfaces directly with the hardware, e.g. device drivers.

2. program construction

   • translators
     • compiler
       • a program that converts high level programs into machine code for execution at a later time (the entire program is converted, not one line at a time as with an interpreter).
       • stages of compilation:
         • Lexical analysis: Comments and unneeded spaces are removed. Keywords, constants and identifiers are replaced by 'tokens'.
           • Symbol table construction: A symbol table is created which holds the addresses of variables, labels and subroutines.
             • Syntax analysis: Tokens are checked to see if they match the spelling and grammar expected, using standard language definitions. This is done by parsing each token to determine if it uses the correct syntax for the programming language If syntax errors are found, error messages are produced.
               • Semantic analysis: Variables are checked to ensure that they have been properly declared and used. Variables are checked to ensure that they are of the correct data type, e.g. real values are not being assigned to integers. Operations are checked to ensure that they are legal for the type of variable being used, e.g. you would not try to store the result of a division operation as an integer
                 • Code generation: Machine code is generated.
                   • Code optimisation: Code optimisation may be employed to make it more efficient/faster/less resource intense.
       • programming errors: logical, syntactical, run-time/execution, linking, rounding, truncation
     • interpreter
       • a program which converts code one line at a time, into machine code and executes it.
     • assembler
       • a program which converts the low level assembly programming language into machine code.

3. IDEs

   • editor
   • automatic colour coding
   • linker
   • automatic line numbering
   • automatic formatting
   • libraries
   • routines/subroutines
   • standard functions
   • Debugger
   • syntax error detection
   • loader
   • break point
   • trace
   • error diagnostics
   • variable watch

4. operating systems

   • An operating system manages hardware and software for a computer providing common services for computer programs.
   • Examples
     • Manages peripherals such as input and output devices
     • Manages printing using spooling
     • Manages backing store
     • Manages memory (RAM)
     • Manages processes
     • Manages security