3 ms·
There's one register called CCR on m68k and CR on PPC, so that's probably not an accident ;)
by jagrsw 3y ago
There's one register called CCR on m68k and CR on PPC, so that's probably not an accident ;)
- adrian_b 3y agoThe term "condition-code register" predates by decades both the Motorola MC68000 (1979) and the IBM POWER (1990). It was a term used in many unrelated computers. Already in 1964, in IBM System/360, the condition-code was a part of a bigger register, the "processor status word". The terms are much older than that. Also in MC68000, the CCR is a part of the bigger status register, which, unlike the CCR, can be accessed only by privileged programs. In POWER, the condition register also holds only the condition-code part of the status, but it has room for 8 groups of condition codes, to allow high speed even for cheaper in-order CPUs, which do not have register renaming (where otherwise a shared condition-code register would prevent the concurrent execution of instructions).
- classichasclass 3y agoYeah, in practical implementations the 32-bit Power condition register is more like eight four-bit ones, and lots of code will run compares in parallel to different fields. It's one of the architecture's notable strengths.