Q. Code Density and Smaller Faster Programs?

Memory was very expensive in older computer. So there was a need of less memory utilization, which is it was cost effective to have smaller compact programs. So it was opined that instruction set must be more complex so that programs are smaller. But increased complexity of instruction sets had resulted ininstruction sets and addressing modes needing more bits to represent them. It is said that code compaction is significanthowever cost of 10 percent more memory is often far less than cost of reducing code by 10 percent out of CPU architecture innovations.

Smaller programs are beneficialsince they need smaller RAM space. Though today memory is very cheap and this potential benefit today isn't so compelling. More significant small programs must enhance performance. How? Fewer instructions mean fewer instruction bytes to be fetched.

Though problem with this reasoning is that it isn't certain that a CISC program will be smaller than corresponding RISC program. In several cases CISC program represented in symbolic machine language may be smaller however the number of bits of machine code program might not be noticeably smaller. This might result from reason that in RISC we employ register addressing and less instruction that require fewer bits in general. Additionally the compilers on CISCs frequently favour simpler instructions so that conciseness of complex instruction rarely comes into play.