On Sat, 27 Dec 2014 09:17:20 -0800, Phil Smith <[email protected]> wrote: >This is fun. I'm not sure modern machines are both microcoded AND millicoded-I >thought millicode was just another form of microcode. Am I wrong?
Sure. Millicode sits between your program and the machine's native instruction set. It is part of the firmware, meaning it can be changed. It primarily intercepts any non-native instruction and breaks it down into a sequence of native instructions or redirects that data to another processor. Microcode is burned into the CPUs, being the on-chip logic that actually runs the native instruction set. In rare cases millicode may intercept a native instruction and re-implement it, such as might be done if an error is found in microcode or chip design too late or too expensive to fix. A z/Architecture instruction may shift from millicode to native and back several times over its life as the underlying chip design changes. Alan Altmark IBM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
