Talk:PDP-8/S - Revision history

Nczempin: /* Clock speed */ maybe this helps

2019-08-19T21:19:28Z

Clock speed: maybe this helps

← Older revision		Revision as of 21:19, 19 August 2019
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	: 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.		: 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). [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 22:34, 19 August 2019 (CEST)		: Yes, the straight-8 is also wrong, per its Maint Manual. I'll write up what I found later (once I fully understand it). [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 22:34, 19 August 2019 (CEST)
			::Okay, I've found something: This clock board <em>can</em> go up to 2 MHz, which doesn't mean that it <em>does</em>: [https://www.pdp8.net/r-boards/pics/r405.shtml]. 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. [http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/r/r405-ds.pdf] [http://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/pdp8docs/dec-08-h6ba-d.pdf?pages=54]--[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 23:19, 19 August 2019 (CEST)

Jnc: But Bell didn't do the PDP-8

2019-08-19T20:34:43Z

But Bell didn't do the PDP-8

← Older revision		Revision as of 20:34, 19 August 2019
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	: 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)		: 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)

	::Intriguing... I assume you are aware that the book I referred to is not by some random chumps; but of course they could have been wrong. I wonder then if the info on the straight 8 is also wrong, given that they're both supposed to have the same clock --[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 21:27, 19 August 2019 (CEST)		::Intriguing... I assume you are aware that the book I referred to is not by some random chumps; but of course they could have been wrong. I wonder then if the info on the straight 8 is also wrong, given that they're both supposed to have the same clock --[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 21:27, 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). [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 22:34, 19 August 2019 (CEST)

Nczempin: /* Clock speed */

2019-08-19T19:28:25Z

Clock speed

← Older revision		Revision as of 19:28, 19 August 2019
Line 11:		Line 11:

	: 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)		: 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)
	::Intriguing... I assume you are aware that the book I referred to is not by some random chumps; but of course they could have been wrong. I wonder then if the info on the straight 8 is also wrong, if they both have the same clock --[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 21:27, 19 August 2019 (CEST)		::Intriguing... I assume you are aware that the book I referred to is not by some random chumps; but of course they could have been wrong. I wonder then if the info on the straight 8 is also wrong, given that they're both supposed to have the same clock --[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 21:27, 19 August 2019 (CEST)

Nczempin: /* Clock speed */

2019-08-19T19:27:28Z

Clock speed

← Older revision		Revision as of 19:27, 19 August 2019
Line 11:		Line 11:

	: 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)		: 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)
			::Intriguing... I assume you are aware that the book I referred to is not by some random chumps; but of course they could have been wrong. I wonder then if the info on the straight 8 is also wrong, if they both have the same clock --[[User:Nczempin\|Nczempin]] ([[User talk:Nczempin\|talk]]) 21:27, 19 August 2019 (CEST)

Jnc: Secondary source is wrong, alas

2019-08-19T13:36:43Z

Secondary source is wrong, alas

New page

==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)