15 Mar
2018
15 Mar
'18
6:15 p.m.
Problems with XCT (execute one instruction): * no clean/obvious semantics; semantics have to be worked out for each different instruction being "executed" * only one level of execute (at least for IBM) * originally used for *tables* of instructions, but what about variable-length instructions? (Similar problem to "skip" instructions) * what are the semantics in the case of interrupts? We now have architectures which support "virtual machines"; analogous problems at much larger scale. At 04:47 PM 3/15/2018, rcs@xmission.com wrote:
PS: Does anyone else miss the XCT instruction? The 7094 & PDP6/10 had it, but it seems to have vanished. I guess it's an architectural nightmare for the hardware folks. --Rich