This was a fantastic explanation so thanks. A couple of questions:
PRF is Physical register file? As opposed to the logical which can point to different backing store(the actual SRAM.)
Register renaming and OoO operations are really enabled by micro-ops? In other words on a CPU with completely hard-wired control unit such things would never be possible.
> PRF is Physical register file? As opposed to the logical which can point to different backing store(the actual SRAM.)
Yep. PRF means the single backing store where all values go, and PRF systems are named for it because they are usually contrasted to the other very common way to implement OoO, ROB-backed systems, where there is a specific location for the final architectural value, and possibly multiple in-progress values in the ROB. Intel used values in the ROB in all their CPUs up to Sandy Bridge, which was their first PRF design.
(The main difference between the types is that ROB-backed is faster in circuit delay, but moves more data than a PRF design, so on the same process they potentially clock higher but produce more heat. PRF-based designs are also easier to scale wider than the ROB-based design.)
> Register renaming and OoO operations are really enabled by micro-ops? In other words on a CPU with completely hard-wired control unit such things would never be possible.
No, you can do renaming and OoO well without uops, it just requires that your instruction set is designed to be amenable to it. Before x86 had uops, it couldn't do OoO and the competing RISC CPUs were way faster because of this. PPro added uops precisely because they made it possible for an x86 cpu to do OoO, and eventually x86 beat all the competing RISC chips at their own game.
> Register renaming and OoO operations are really enabled by micro-ops? In other words on a CPU with completely hard-wired control unit such things would never be possible.
No, they're orthogonal concepts. The first OoO processor (the System 360 model 91) didn't have uops.
Wow, this is kind of blowing my mind that they were doing this with a hard-wired control unit in 1969(I think I have the date right.) Big Blue, its easy now a days to forget just how amazing they were. Do you have links you can recommend? Thanks.
PRF is Physical register file? As opposed to the logical which can point to different backing store(the actual SRAM.)
Register renaming and OoO operations are really enabled by micro-ops? In other words on a CPU with completely hard-wired control unit such things would never be possible.