2.5

• Machine code is a series of numbers, written in either binary or hexadecimal.
• The instructions that tell a computer what to do are written in machine code.
• High level programming languages are languages that are close to the spoken and written language of the programmer.
• Programmers find machine code difficult to learn, program in and debug. As a result, the majority of programmers write programs in high level programming languages.
• Programmers write in high level languages because they are easier to understand and are less complex than machine code.
• High level languages are restricted to the number of statements built into them.

  If the programmer wants a program to do something, but a statement does not exist to do so, the task cannot be done.
• Any program written in a high level language is known as source code.
• Source code must be translated into machine code before the computer can understand and execute it.
• Low level languages are languages that sit close to the computer's instruction set.
• Writing in machine code allows programmers to do things that might not be possible in a high level language.
• Machine code is notoriously difficult to write in, understand and debug, simply because it consists of either binary or hexadecimal numbers.
• Assembly language sits between machine code and high level language. While high level languages use statements to form instructions, assembly language uses mnemonics.
• A compiler takes the source code as a whole and translates it into object code all in one go.
• Advantages of compilers


  • Compiled programs run quickly, since they have already been translated.
  • A compiled program can be supplied as an executable file. Since an executable file cannot be easily modified, programmers prefer to supply executables rather than source code.
  • Compilers optimise code. Optimised code can run quicker and take up less memory space.
• Disadvantages of compilers


  • Because the source code is translated as a whole, there must be enough memory space to hold the source code, the compiler and the generated object code.
  • Compilers do not usually spot errors.
  • The source code must be re-compiled every time the programmer changes the program.
• An interpreter translates source code into object code one instruction at a time.
• Advantages of interpreters


  • Instructions are executed as soon as they are translated.
  • Since instructions are executed once translated, they are not stored for later use. Interpreters require less available memory.
  • Errors can be quickly spotted - once an error is found, the program stops running.
• Disadvantages of interpreters


  • Interpreted programs run more slowly as the processor has to wait for each instruction to be translated before it can be executed.
  • Additionally, the program has to be translated every time it is run.
  • Interpreters do not produce an executable file that can be distributed. This could be modified without permission.
•  An executable file is a file that is ready to run. An executable file cannot be easily modified.
• Editors are software which allow programmers to write and edit code.
• Editors have special tools. These help to improve the readability of code.
• IDEs usually contain error diagnostics which will highlight syntax errors in real time as you program.
• The run-time environment allows you to run programs to test how well they work.