Instruction Set Architecture

Four Types of ISAs.

Why are Registers Good?

There are three reasons for prefering register operands to memory operands. Registers are faster than memory, they reduce memory and interconnect traffic, and they are more compact when naming them. A 32-register architecture only requires 5 bits to name a register, while it requires between 30-40 bits to name a memory location.

Addressing Modes

The addressing modes specifies how a particular instruction operand should be interpreted. There is a large number of addressing modes but the important ones are: Most RISC processor only support these three addressing modes. All other addressing modes can be constructed from these. For Immediate and Displacement modes it is important to know how big the Immediate and Displacement numbers can be. Most processors use 16 bits. If you want larger immediate number you have the use the LUI instrustion which loads a 16-bit immediate number on the top 16 bits of a 32-bit register.

Types Of Instructions