Talk:Microprocessor Design/Instruction Set Architectures

alternatives to single Program Counter

Microprocessor Design/Instruction Set Architectures mentions "there are processor architectures, for instance the CDP1802, that do not have a single Program Counter" [1]

The Wikipedia: RCA 1802 certainly proves it is not *necessary* to have a special PC register separated from the other registers. What other processor architectures do not have a single Program Counter?

--DavidCary (talk) 04:29, 5 August 2009 (UTC)

I'll grant that there are not many out there. The 1802 had a register that was set to be the program counter by convention, and another that was used by convention for subroutine calls. But any GP register could act as program counter. If we go back to archaic computing, there were a number of computers without static storage that did not have a program counter at all, but rather the instruction would end with the address of the next instruction; program store was a spinning drum, and the last word of the instruction was the encoded position on the drum surface of the next instruction. In the PDP-11, one of the registers, R7, was the PC by convention; I am unsure whether that was convention only or could be changed in software. That is, however, all I can remember off the top of my head. Chazz (talk) 06:43, 5 August 2009 (UTC)