Programming languages

• Machine Code


  the instructions that tells a computer what to do
• machine code is a series of numbers written in binary


  each number represents a different instruction
• programmers find reading machine code difficult


  as a result programmers chose to write in high-level languages e.g python, VB,
• High level languages must be converted into machine code


  This is done by compilers, interpreter, assembler
• Source code


  term given to a set of instructions that are written in human readable programming languages. Source code must be translated into machine code before a computer can understand and execute it
• Low level languages


  languages that sit close to the computers instruction set (instructions a processor can understand)
• types of low level languages


  machine code

  assembly language
• Assembly Language


  uses mnemonics to form instructions that directly corresponds to machine code
• a program written in a high level language is known as


  source code
• Translator


  Converts source code (high level language) into machine code that a CPU can understand
• Compiler


  takes the source code as a whole and converts it into machine code all in one go. Once converted the object code can be run unassisted at any time
• Advantages of Compilers


  -runs quickly as they have already been translated

  -program can be supplied as an executable file

  -it is optimised code, so will run quicker and take up less memory
• Disadvantages of compilers


  -must be recompiled every time the programmer changes the program

  -source code compiled on one platform cannot be run on another, specific to the processor's architecture
• Interpreter


  translates source code into machine code one instruction at a time and is then executed immediately
• Advantages of interpreters


  -instructions are executed as soon as they are translated

  -errors can be quickly spotted as the program stops the second the error is found and identifies the issue
• Disadvantages of interpreters


  -programs run slowly as the processor must wait for each instruction one at a time

  -program must be translated every time for it to run

  -does not produce an executable file than can be distributed

  -do not optimise code
• assembler


  translates assembly language into machine code