ISA is also known as Computer Architecture.
There are two styles of Instruction Set Architecture.
CISC or Complex Instruction Set Computer. CISC instruction carries a lot of information and does a lot of work.
RISC or Reduced Instruction Set Computer has a number of small instructions that can be carried out quickly and do not contain a lot of information in a single instruction. It needs to execute multiple small instructions to achieve the same effect as a CISC instruction.
Modern-day CISC based chips consist of one complex instruction performing several tasks, which is decoded into many small RISC-like instructions each performing one individual task. It actually feels like the modern day CISC chips are somewhat like RISC based chips.
In the past, to improve the performance of a computer the companies tried to improve the clock frequency and reduce the number of instructions.
In the 1960s, Gordon Moore the CEO of Intel published a paper in which he predicted that the number of transistors on a manufacturer’s die was double every 18 months, which is known as Moore’s Law. It has been proved to be right for several decades.