What is an ISA?

The Instruction Set Architecture (ISA) Is Group Of Commands Inbuilt Into The Processor's Microarchitecture.

The ISA Defines The Set Of Machine Instructions That Processor Can Directly Decode And Execute

ISA can only be understand by Assembly language programmer or a compiler writer.

We write commands in ISA which computer performs accordingly as we order them.

We write a program in high level language like C, C++, Java etc. This high level instructions needs to be converted into assembly language so that machine can understand instructions But machine is a combination of electronic circuits that can only understand zeros and ones so finally assembly code is converted into object code that is machine understandable with the  help of assembler and compiler.

Instruction Set Architecture

The computer ISA defines all the programmer-visible components and operations of the computer

Memory organization

  • address space-- how may locations can be addressed?
  • addressibility -- how many bits per location?

Register set

  • how many? what size? how are they used?

Instruction set

  • opcodes
  • data types
  • addressing modes

ISA provides all information needed for someone that wants to write a program in machine language (or translate from a high-level language to machine language).