On 07/15/2015 10:48 AM, Jay Jaeger wrote:
Lots of machines supported variable length operands (like the machine you reference in the link, IBM S/360, Burroughs, etc. etc. However, machines with variable length instructions not split into any kind of word boundary are not as common.
Sure, but that doesn't mean that they didn't exist. As a matter of fact, the machine I cited was *bit*-addressable. That doesn't imply that any datum was absolved of some sort of alignment. But yes, you could have bit fields overlapping word boundaries--let's see your 1410 do that...
I really don't see much of a fundamental distinction between the 1401, 1410, 7080 or 1620 or any other variable word-length machine of the time. One really have to ask oneself "why variable word-length?" when it costs so much in terms of performance. I believe that it's mostly because memory was very expensive and it was viewed as a way of coping with that issue.
FWIW, Dijkstra disliked the 1620 immensely. I don't recall his opinion of the 1401.
--Chuck
