Processor instruction sets

• Low-level languages use the specific instruction set of a processor. The instruction set for each processor is defined by the manufacturer, meaning low-level languages can only be executed by a processor of the same type that it was written for. For this reason, code written in low-level languages is non-portable and will not run on computers with a different processor.
• There are two types of low-level programming language: machine code and assembly code.
• Designing a processor


  Manufacturer decides which operations the processor will be able to carry out
• Instruction set


  Set of instructions that allows a programmer to use the operations the manufacturer has designed
• Instruction sets will only work with that particular processor, or a set of processors that share the same operations (called a processor family)
• Processor instruction set


  • Provides commands to allow the low-level programmer to move data into and out of the processor
  • Allows the low-level programmer to make use of the processor's internal registers to minimise data transfer
• The low-level programmer must have a good understanding of the design and capabilities of the processor
• If a programmer understands a processor well enough, low-level languages allow them to write extremely efficient programs that make the most of the processing power and memory available