Historical Notes on CISC and RISC: Difference between revisions

('''NB''': I originally wrote this for some of the other students in an assembly language class I took in Fall 2006. While it is not about OS-dev per se, it may help clarify some of the puzzling aspects of assembly language for some members. - [[User:schol-r-lea]])

 

 

To understand why how this reversal came about, you need to know a bit of history. When stored-program computers based on the Von Neumann architecture were first being developed in the late 1940s and early 1950s, the size and complexity of the hardware (which was much more diverse than today, using such disparate technologies as mercury delay lines, CRT-phosphor memories, magnetic drums, wire and tape recorders, ferromagnetic cores, and the ever-present vacuum tubes) meant that the hard ware capacities were extremely limited; it was not uncommon for even a large machine to have only one or two registers and a main memory of a few thousand words (which varied in size from machine to machine). The instruction sets were equally constrained, and often had special-purpose instructions for connecting to the peripherals, taking up the already small instruction space.