FPGA VAX update (CDC song)

On 11/3/2005 at 12:26 PM Paul Koning wrote: UGH! That was the long "stranger" tape driver overlay to 1MT. Ugly beast, too--and an exercise in futility. 30 years ago, I spent entirely too much time trying to make it run for some stupid benchmark. This was back on the 607's. You had to read the tape and write to CM at the same time. Lose your place in the pyramid and you had to backspace to the beginning of the record and try all over...and over...and over...again. Since the PPU's on the 7000 had hard-wired buffer areas in CM, they couldn't access all of CM. So the burden of the OS fell on the CPU. 7000 SCOPE used a very clever system of staggered RA's and overlapping FL's for different levels of privilege. So, the job supervisor task had an FL that included itself and the FL of the job it was supervising, but its code and RA was placed immediately below the job, so it had unrestricted access to the job's FL. Same sort of idea for the buffer and I/O managers. Very clever implementation before protection "rings" got the credit for the idea. Good luck with 1LT--there's been much hair left on the floor from folks who worked on that thing. Cheers, Chuck