Chapter 8

Chapter 8

1. Machine Code

   • Processors only understand machine code
   • Sequences of binary
   • Machine code needs to be rewritten for different processors

2. Assembler

   • Assembly code uses mnemonics to represent binary sequences
   • Converts assembly code to object code
   • Assembly code isn't very portable

3. Compiler

   • Converts high-level code into object code.
   • This code can be distributed to any compatible system
   • Once compiled code can be ran any number of times and faster that an interpreted program
   • Compiled code is non human readable

4. Interpreter

   • Takes each line converts it into machine code then runs it
   • Slow to run since the user has to wait for each line to be interpreted before it can be ran
   • Can lead to the same line being interpreted multiple times

5. Object Code

   • Intermediary step before pure machine code produced.
   • Placeholders where library code needs to go
   • Once a linker is used machine code is produced.

6. Compiler

   • Lexical analysis
     • White spaces removed
     • high level code turned into tokens
     • Compiler picks out reserved words
     • Variable names added to symbol table
   • Syntax analysis
     • Checks code follows valid syntax
     • List of syntax errors generated
     • Abstract syntax tree produced
     • If tokens don't fit in the tree then there is a syntax error
   • Code generation
     • Compiler converts abstract syntax tree into object code
   • Optimisation
     • Removes pointless lines of code
     • Makes the code more efficient

7. Libraries

   • Contain code to complete complex tasks that can be reused
   • Library is used through an application programming interface.

8. Static linkers

   • Library code added directly into program when compiled
   • Means final program may be large in size

9. Dynamic linkers (Loaders)

   • Compiled versions of the library are stored and the operating system links a program to them when it is run
   • A loader is part of the OS and is responsible for loading a program into memory.