On 07/04/2015 09:42 AM, Diane Bruce wrote:
Both Apollo and SUN did this. The clocks were two phase so one ran behind the other. It was a hack.
I don't remember when I first saw the 68000 in detail--perhaps it was at a WESCON in the late 70s. My 68K manual is from that show and I took some time to actually sit down and read the first couple of chapters at the show. The mention of a supervisor mode and faulting on undefined addresses (bus faults, actually) got me very excited and immediately sent visions of virtual memory spinning.
I went back to the guy at the Motorola sales booth and asked him about the prospect. He sighed and rolled his eyes a bit and said that I must have been the hundredth person to ask about the subject that day. He did his best to gently break it to me that not all instructions could be restarted from a bus fault--the CPU simply didn't save enough information to make that possible.
The following year, there were a number of Unix boxes being shown that used the 68K, advertising that they were real competition for traditional minis. Against my better judgment, it was decided that the the system to supplement our VAX 11/750 setup would be a Plexus box.
That was a mistake, as I predicted. The box became the butt of jokes about its lack of performance.
--Chuck
