View source for Talk:PDP-8/S

==Clock speed==

"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." [[User:Nczempin|Nczempin]] ([[User talk: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. [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 15:36, 19 August 2019 (CEST)