I/O models (was RE: Happy Birthday VAX 11/780 (influence of))

OK, it's fair to say that there's nothing that precludes memory-mapped I/O in any machine (except perhaps physical memory architecture, although I can't think of an example). But port-mapped I/O machines had specific instructions for I/O, which might well facilitate the process beyond the simple mechanics of memory-mapped I/O (think about polling on a skip flag on a PDP-8) but also potentially limited one in either range or capability. It's also important to recognize that the PDP-11 *enforced* memory-mapped I/O in an upper region, which limited working store (and it was not the only machine to do so, e.g. Alto). And we're discussing this because...? :-) ________________________________________ From: cctalk-bounces at classiccmp.org [cctalk-bounces at classiccmp.org] On Behalf Of Dave McGuire [mcguire at neurotica.com] Sent: Friday, October 29, 2010 10:31 PM To: On-Topic and Off-Topic Posts Subject: Re: Happy Birthday VAX 11/780 (influence of) On 10/29/10 4:55 PM, Tony Duell wrote: He certainly did, I remember that article well. He started the article by relating a conversation that he'd had with a fellow computer guy, and they were arguing (I think) 6800 vs. Z80. He said something like "When he said the 6800 had memory-mapped I/O and the Z80 didn't, I knew he didn't know what it was". :) -Dave -- Dave McGuire Port Charlotte, FL