Design flaw in the SCSI spec?

With his express permission, I'm forwarding a mail from a public list. I am interested in Gene's comments about the design of SCSI, but I don't know enough electronics to judge. I thought others here might. I have trimmed the mail a little to the relevant parts. -- Liam Proven - Profile: https://about.me/liamproven Email: lproven at cix.co.uk - Google Mail/Hangouts/Plus: lproven at gmail.com Twitter/Facebook/Flickr: lproven - Skype/LinkedIn: liamproven UK: +44 7939-087884 - ?R (+ WhatsApp/Telegram/Signal): +420 702 829 053 ---------- Forwarded message --------- From: Gene Heskett <gheskett at shentel.net> Date: Wed, 8 Jan 2020 at 17:29 Subject: Re: External Disk Intrusion To: <ubuntu-users at lists.ubuntu.com> On Wednesday 08 January 2020 09:01:35 Liam Proven wrote: [...] And all that pickityness can be laid at the feet of a bean counter between the interface card designer, who specified a $2.00 schotkey diode for buss isolation, which had a maximum voltage drop across it of perhaps .1 volts, and changed to have an 8 cent Si diode with .666 volts drop across it, thereby lowering the logic one voltage by .45 volts. Since the logic one at the logic chips inputs had to be at lease 2.2 volts, and the nearest set of termination resistors gave 3.0 volts when this buss isolation diode was replaced with a short, but with the cheap Si diode in there gave a logic one voltage closer to 2.4 most of the circuits noise margin was used up and considering that same bean counter crossed out the 5% terminators in favor of 20% tolerance, the result was predictable. The situation was much better when active terminations came into use, but by that time the scsi buss's reputation was doomed. But back in the day of the bottom 190 market tv stations were generating their on air gfx needs with a bank of Amiga computers, every scsi card that came in the door, if the engineer was worth his paycheck, that diode was replaced the first time the Amiga it was in, crashed. End of problem except for one Trump Card, where in traceing that card, I found the termpacks had been soldered in bass ackwards. It was easier to cut and jumper the supplies traces than to unsolder the packs and turn them around. So I did that in addition to swapping out the infamous diode. We, in a middle 160's market, were the first to put our news on the air, out as a webpage, which led to legal problems because CBS fussed about their copyrights, so we had to filter any web content that came from CBS, but that didn't last long after their bean counters discovered there was money to be made. That was all driven by ARexx and delivered by dialup from that Amiga in those Jurrasic (in web time) days. Who am I to criticise the makers of that stuff? I have an 8th grade diploma, but I am also a CET. Look that up if you care. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> -- ubuntu-users mailing list ubuntu-users at lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-users