stem/CS/Code Types.md

Machine Code

• Machine language instructions
• Directly control CPU
• Strictly numerical
• Lowest-level representation of a compiled or assembled program
  • Lowest-level visible to programmer
  • Internally microcode might used
• Hardware dependent
• Higher-level languages translated to machine code
  • Compilers, assemblers and linkers
  • Not for interpreted code
    • Interpreter runs machine code
• Assembly is effectively human readable machine code
  • Has mnemonics for opcodes etc

Microcode

• Layer between CPU hardware and instruction set architecture
• Normally written during design phase
  • Deployed to ROM or PLA
    • Programmable logic array
• Machine code often has some backward compatibility
  • Microcode is circuit specific

Byte Code

Portable Code

• Efficient execution by interpreter
• Compact numeric codes, constants and references
  • Encode compiler output following analysis and validation
• Can be further compiled
  • JIT
• Typically passed to VM
  • Java, Python

Object Code

• Product of compiler
• Sequence of statements
  • Machine code
  • Intermediate
    • RTL
• Linked to form executable
  • Object code portion of machine code not yet linked