Talk:S-100 bus

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[edit] Comart (UK)

Comart Computers in Britain made a range of S-100 based machines: There was the single-user Z-80 based 'Communicator', and multi-user x86-based machines that ran Concurrent CP/M-86 and possibly Concurrent DOS 386. I wish I could remember more of the details, but the "C-frame" (was this a codename?) had Voltage regulators on each card and ran 18V and 9V down the backplane and the "K-frame" ran 12V and 5V down the backplane and had wire links where the regulators would have been (some cards were common to both series).

[edit] Misc Note

The author of the S-100 page states "A deal on power supplies led to the use of +8 V and +18 V, which had to be "pulled down" on the cards to TTL (+5v) or RS-232 (+/-12 V) levels." I believe the actual reason for these voltages was to allow for on-card voltage regulation. +8v and +18v would have been sufficient to drive the linear regulators of the time (such as the 7805 and 7812). I'm fairly sure I can remember photos of S-100 cards that had these regulators onboard.

Yes. This sort of setup was quite common in electronics of the time. One advantage would be that with separate regulators for each card, the regulators could be smaller, simpler, and grow with the system (instead of having to build one big regulator for an entire system, including room for future expansion) and there'd be better isolation among cards because power transients from one card would have to propagate through both cards' regulators before getting to another card, instead of just through a shared and relatively unfiltered power bus. The article's current "ha ha, what idiots they were to design this way" slant is both stupid and unencyclopedic.

Now that DC-DC converters are common and cheap, there's less need for power to be distributed at a higher voltage than it'll be finally used to give the regulators headroom, but it's still the case that individual boards, subsystems, and chips in a modern computer will often recondition or reregulate incoming power before using it. 129.97.79.144 16:18, 2 October 2007 (UTC)

Also, on-card regulators eliminate a greeat deal of the risk which came from the placement of the different voltage supply lines on the bus (which are worngly called a "disaster" in the article). The danger was a short between the lower and the higher voltage line, possibly causing low voltage components receiving excess voltage. The regulators would provide some level of protection, probably failing at some point, but, being sort of inexpensive, not causing very much grief (I guess).

Modern busses would are more prone ot a short between a voltage supply line and ground instead, therefore more likely to lower/eliminate a supply voltage instead of raising it (with also a chance of "frying" the regulators in the PSU). --80.134.51.117 (talk) 13:32, 21 December 2007 (UTC)