On Sun, 28 Dec 2014 05:55:09 -0800, Phil Smith <[email protected]> wrote: >Alan, by that definition, none of us have ever applied a microcode patch. Yet >I remember distinctly doing so (box after box of 1.44MB floppies!). > So either IBM has changed the meaning of the term, which doesn't quite make > sense, or I was hallucinating. Plus I'm not sure what the distinction >would be between microcode and the actual raw chip instruction set in this >case?!
Technically, microcode is what decodes instructions, puts data on the buses, moves data into and out of registers, and turns the logic gates on and off. It need have no similarity to what you read in a programming reference. When we first started using the word "microcode" I believe it was correct. Then we split the microcode into a burned-in part and a loadable part, so the word came to mean "reloadable microcode." Feh. It was no longer really microcode, but there wasn't a term for what it was. So we introduced the term "millicode". As the CPU architecture got more and more complex and functionally rich, "microcode" was left to flounder with no clear meaning. So today we have "firmware" that is an accretion of all of the things that can be changed without replacing parts, "millicode" to identify the firmware that implements the architecture, and "microcode" to mean "everything that isn't millicode." Yet you never hear "millicode" being applied to storage controllers or other parts outside of the processor. And you know as well as I do that they aren't replacing microcode on the processor chips. They're replacing the OS and the applications that use them. But we continue to call it "microcode." The joke's on us.... If you try to create clear-cut definitions of the terms, you will be frustrated. It's best to go read what Humpty Dumpty has to say to Alice about the meaning of words. When I hear them, I wait for context to surface and then just say to myself, "Oh. THAT part of The System." :-) Alan Altmark IBM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
