You may not be looking for the right thing. On the aforementioned CSP, the instruction that performed XOR was called "XR" and not "XOR". My source is firsthand knowledge; I was a CE and performed service calls on the System/34, System/36, 370, and 390.

In any case, I am describing equipment built mostly in late 60s through the late 70s at IBM Rochester and Poughkeepsie. The IBM PC was developed by an entirely different team at IBM Boca Raton, and IBM didn't design its CPU.

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rep_lodsb 2 hours ago | parent [-]

I don't doubt that this specific processor special-cased XOR (regardless of how it was called in the assembly language)!

Merely pointing out that where both operations were available, there seems to have been a preference to use SUB instead, with some continuity from early business-oriented mainframes, to the 360, to the PC.

	▲	fweimer an hour ago \| parent [-]
		You probably would prefer to use SUB with fault-checking to clear registers in general-purpose code, and only use XOR in early startup (and perhaps fault handlers), where error checking has to be suppressed. So both observations seem to align well?