PDP era and a question

please see embedded remarks below. Dick -----Original Message----- From: Tony Duell <ard(a)p850ug1.demon.co.uk> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Friday, August 27, 1999 1:04 PM Subject: Re: PDP era and a question the of finish. It depends more on how you define "can't" than anything else, though. I had the same feeling when just about all the useable CAD/CAE software was limited to VMS and UNIX. I bought and limped along with what I could get for the PC, back then using DOS and customized drivers for the appropriate display, which, back then, alone, cost about as much as my then new logic analyzer. What that is, Tony, is a matter of preference. YOU have to decide where YOU spend your money. In yesterday's newspaper I noted that the local discount house (Best-Buy for those who care) was offering a major-brand 350 MHz Celeron-based computer system without monitor but with AGP video, 6.4 GB HDD, 64 MB memory, CDROM, FDD, v.90 modem, keyboard, all for $399 US. A really nice (I recently bought one when the "appropriate display" (19") mentioned above developed a margin problem.) 17" monitor for $199. That means that for what I typically earn in a couple or three days after taxes and expenses, I can buy a whole computer system capable of doing this FPGA stuff. I recently read that the folks who sell these FPGA's have no problem at all giving you the necessary data to enable you to configure their parts. They won't give you a disassembly tool or whatever that would be, but they'll tell you enough so you can build your own configuration tools to support their parts. They won't hold your hand and they won't debug your work, but they will give you a spec so you don't have to buy their software or use it. I bought a 20-year old 250 MHz 'scope not long ago with what that system at Best Buy would cost. Now, I shopped for a year in order to find the thing, but that's what I got for $600. All software is open-source if you have the dough to buy the sources. Not all of us are willing to pay the required 6.23*10^23 bucks for what we'd otherwise get for less than $1k for just the objects. Again, it's just a matter of preference. Most people get by this hurdle with little trouble. or clever in in There's a brocheure lying about here somewhere from a company which offers a XILINX look-alike which operates with delays of about half those of the fastest XILINX, though there's some question about the universality of that claim, but they certainly explain why their routing delays are shorter. Prop-delays of 1ns are claimed for the combinatorial logic in several vendors' parts, and the claim of 25 MHz for 7400-series TTL was quite generous. It would propagate into a light load and single flops would keep up at 25 MHz. I remember a countdown chain which generated a bunch of system timing from a 24.576 MHz clock, which was a harmonic of nearly all the telecom clocks as well as baud rates. That one didn't work until one substituted 74S-series TTL. HTTL and LSTTL wouldn't do it. The clock-to-Q of the flops just wouldn't meet the required setup times. Now, it worked fine once we rebuilt the counter chain so it ran at half that rate. Lots of '70's TTL MSI would work at rates in excess of 30 MHz, but only for small circuits. You could run one shift register at that rate, but if you needed to shift longer words, you might be in trouble. It was even worse with counters. If you then needed to decode the outputs of a 16-bit counter . . . you see my point, I'm sure. These same problems are encountered in FPGA's, but the circuits whose timing is critical can be planned out in such a way that the penalties for routing delays are minimized. What's more, because adding a pipeline register doesn't mean putting another package on the board, you can do that. Pipeline registers increase operating frequency while increasing the latency. They make decoding much safer.