Q. Fundamental issues of concerns for instruction set design?

A number of fundamental issues of concerns for instruction set design are:

Completeness: For an early design the primary concern is that the instruction set must be complete that means there is no missing functionality which means it must include instructions for the fundamental operations which can be used for creating any possible execution and control operation.

Orthogonal: The subordinate concern is that instructions should be orthogonal which means not unnecessarily redundant. For illustrationfloating number operation and integer operation generally aren't considered as redundant however different addressing modes may be redundant when there are more instructions than essentialsince the CPU takes longer to decode.

An instruction format is used to describe the layout of bits allocated to these elements of instructions. Additionally the instruction format implicitly or explicitly signifies the addressing modes used for every operand in that instruction.