From Computer History Wiki
"Computer Structures: Readings and Examples", page 120: "A PDP-S/S is one-fifteenth of a PDP-8 at one-half the cost. ...even though the same 2-megahertz logic clock is used in both cases." Nczempin (talk) 17:32, 18 August 2019
- It's probably best not to rely on secondary sources like that, when real manuals are available - because in this case, they got it wrong. From the "PDP-8/S Maintenance Manual" (F-875, August 1969), "Word Times" (Section 2.2, pg. 2.7):
- Each word time is made up of 14 bit times .. during which the clock generates a string of fourteen bit pulses 750 ns apart.
- The basic bit clock is therefor 1.333 MHz, whereas the word clock is 95kHz.
- There can be up to 6 'word times' during the execution of an instruction, or as little as 3 ("fetch", "execute", "end"), depending on the type of instruction, and what else is going on in the machine ("break" word time, for interrupts).
- There could be an interesting discussion about what "clock speed" should refer to; Template:Infobox Machine says it is "CPU cycle time", which for the -8/S is probably the 'word time'. Since it's a bit-serial machine, probably best to give both. Jnc (talk) 15:36, 19 August 2019 (CEST)
- Well, Bell didn't do the PDP-8, he was the PDP-6 and PDP-11; the PDP-8 was Edson DeCastro, later of DG. So he's probably not familiar with the details, right off the top of his head.
- Yes, the straight-8 is also wrong, per its Maint Manual. I'll write up what I found later (once I fully understand it). Jnc (talk) 22:34, 19 August 2019 (CEST)
- Okay, I've found something: This clock board can go up to 2 MHz, which doesn't mean that it does: . And I'm assuming they were referring to the board by "the same 2-MHz clock". So it's basically a potentially 2 MHz clock that's actually run at 1.33 MHz, as far as I understand. I would argue that talking about 2 MHz is a bit misleading then, though.  --Nczempin (talk) 23:19, 19 August 2019 (CEST)