Computer History Wiki - User contributions [en]

Talk:PDP-8

2019-08-26T09:09:32Z

Nczempin:

==Clock speed==

From the "PDP-8 Maintenance Manual" (F-87, February 1966), "Major States", "Time States" (pg. 1-9, 1-10):

: ''The computer enters one major state during each 1.5 usec computer cycle''
: ''Two major time states, .. T1 and T2, occur during each computer cycle (or major state)''

and "Clock and TG Flip-Flop" (pg 3-4):

: ''produces standard positive 100-nsec pulses at a rate at a repetition rate of 1,333,333 pps. Each positive pulse complements the TG flip-flop''

This is a bit confusing, but it seems that the basic clock is 1.333 MHz, but that there are a pair of those ticks (T1 and T2) during each major state, which agrees with the timing given for major states, which is at a rate of .6666 Mhz.

Given that, as before, "clock speed" should refer to "CPU cycle time", I'd say we should go with 'major state time' for "cycle time".

And maybe we should change the caption in the info-box to say "cycle time", to better inform readers of what the field is? [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 17:35, 20 August 2019 (CEST)

Oh, the major state types which may be traversed during an instruction are:

* Fetch - this may be the only one for simple instructions
* Defer - during indirect addressing
* Execute - all memory reference instructions except JMP
* Word Count - 1st cycle of [[OMNIBUS|three cycle data break]]
* Current Address - 2nd cycle
* Break - 3rd cycle; or single cycle data break

So really most instructions will be one to three major states. [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 18:32, 20 August 2019 (CEST)

: OK, I've changed the [[Template:Infobox Machine‎|template]]; will do the article 'soon' (to give people a chance to comment). [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 14:25, 22 August 2019 (CEST)

:: Not sure I follow the reasoning behind all this. The clock speed is simply the frequency of the clock, which I'm fairly convinced we've deduced to be 1.33 MHz. It is "externally visible", and it the basis for such measures as [https://en.wikipedia.org/wiki/Cycles_per_instruction "cycles per instruction" ]. Why are we getting rid of it? --[[User:Nczempin|Nczempin]] ([[User talk:Nczempin|talk]]) 18:19, 23 August 2019 (CEST)

: I gave the reasoning in [[Template talk:Infobox Machine]], I guess you didn't have a chance to look?
: The problem is that 'clock speed' doesn't really give a good sense of how fast a machine is (it all depends on how many clock ticks per instruction, which differs from design to design), whereas 'cycle time' is further up the architectural ladder, and so more likely to be something one can compare across machines to give a relative sense (although admittedly it has issues of its own).
: And the low-level internal clock is not necessarily "externally visible" - e.g. the multi-phase clocks in the [[LSI-11 chip set]], [[KB11]], etc are completely invisible even at the instruction level.
: But we could easily have ''both'' 'clock speed' and 'cycle time', if you see some utility to having the low-level clock speed documented. I wouldn't want to have ''just'' clock speed, though. [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 19:40, 23 August 2019 (CEST)
: The -8 and -8/S are a perfect example of how misleading 'clock speed' is, in terms of machine performance! They both have a 1.3333MHz clock, but... :-) [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 23:46, 23 August 2019 (CEST)
:: I don't feel strongly either way about "cycle time", but for me clock frequency is a starting point that seems ubiquitous. Of course clock frequency does not directly equal performance. I don't think I understand the [need for a] distinction between "cycle time" and "memory speed" --[[User:Nczempin|Nczempin]] ([[User talk:Nczempin|talk]]) 11:09, 26 August 2019 (CEST)

Talk:PDP-8

2019-08-23T16:19:21Z

Nczempin: /* Clock speed */ why remove clock speed?

PDP-8

2019-08-19T21:24:22Z

Nczempin: fpund good sources (primarily maintenance manual) that clarifies this

''This article is about the first PDP-8, which had that name without a model suffix. For information about PDP-8's in general, see [[PDP-8 family]].''

{{Infobox Machine
| name = PDP-8
| image = PDP-8.jpg
| caption = An original, transistorized PDP-8
| manufacturer = [[Digital Equipment Corporation|DEC]]
| form factor = [[minicomputer]]
| word size = 12 bits
| year introduced = 1965
| year discontinued = 1969
| architecture = [[PDP-8 architecture|PDP-8]]
| physical address = 32k words (requires optional Type 183)
| virtual address = 4k words
| design type = [[clock]]ed random [[logic]]
| clock speed = 1.33 MHz
| memory speed = 1.5 μseconds
| memory mgmt = bank select
| logic type = [[diode transistor logic|DTL]]
| bus arch = Negative I/O Bus
| predecessor = [[PDP-5]]
| successor = [[PDP-8/I]]
| price = US$18,500

}}

The '''PDP-8''' (now often known as a '''Straight 8'''; the name dates from the late 60's, apparently adopted to allow disambiguation), the first model of the [[PDP-8 family]], was [[Digital Equipment Corporation|DEC]]'s major breakthrough, and now considered the first really successful [[minicomputer]]. It was, by a significant amount, the cheapest computer yet made at the time.

The PDP-8 was constructed with discrete [[transistor]]s, packaged into DEC's [[FLIP CHIP]] technology. It could perform an addition to the [[accumulator]] in 3.0 μseconds, and a 12 by 12 bit multiplication with 24 bit result in 15 μseconds (average; range 9 to 21), using the optional math extension hardware (below).

==Options==

Options included:

* Type 183 Memory Extension Control, which was needed to support more than 4k [[word]]s of memory
* Type 184 Memory Module
* Type 188 Memory Parity
* Type 182 Extended Arithmetic Element, which supported [[hardware]] integer multiplication and division, multi-[[bit]] double-word shifts, and [[normalization]]

== Operating Systems ==

The PDP-8 could run various operating systems including:
*[[OS/8]]
*[[TSS/8]]
*COS-310

== Emulators ==

There are various emulators for PDP-8 systems including:

*[[SIMH]]

== Application software/Simulation software ==

Mention in this video regarding a PDP-8 screen running J.H. Conways game of life:

* [https://www.youtube.com/watch?v=R9Plq-D1gEk Inventing Game of Life - Numberphile]

{{Nav PDP-8}}

[[Category: PDP-8s]]
[[Category: DEC Systems]]

Talk:PDP-8/S

2019-08-19T21:19:28Z

Nczempin: /* Clock speed */ maybe this helps

==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)

::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)
::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)

Talk:PDP-8/S

2019-08-19T19:28:25Z

Nczempin: /* Clock speed */

Talk:PDP-8/S

2019-08-19T19:27:28Z

Nczempin: /* Clock speed */

PDP-8/S

2019-08-18T17:35:59Z

Nczempin: see "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."

{{Infobox Machine
| image = PDP-8-SFrontPanel.jpg
| caption = PDP-8/S [[front panel]] inlay
| name = PDP-8/S
| manufacturer = [[Digital Equipment Corporation|DEC]]
| form factor = [[minicomputer]]
| word size = 12 bits
| year introduced = 1967
| year discontinued = 1970
| architecture = [[PDP-8 architecture|PDP-8]]
| physical address = 32k words (requires optional MC8S)
| virtual address = 4k words
| design type = [[clock]]ed random [[logic]]
| clock speed = 2 MHz
| memory speed = 8 μseconds
| memory mgmt = bank select
| logic type = [[diode transistor logic|DTL]]
| bus arch = Negative I/O Bus
| predecessor = [[PDP-8]]
| successor = [[PDP-8/L]]

}}

The '''PDP-8/S''' was [[Digital Equipment Corporation|DEC]]'s attempt to produce a 'cheaper' [[PDP-8]]. It was a [[serial computer|serial]] implementation, which reduced the part count somewhat, but resulted in an incredibly slow machine, compared to the rest of the line. It was soon discontinued.

The PDP-8 was constructed with discrete [[transistor]]s, packaged into DEC's [[FLIP CHIP]] technology. It could perform an addition to the [[accumulator]] in 64 μseconds. It had [[parity]] on the [[main memory]] as standard, not optional.

==Options==

Options included:

* DB8S Data Break, needed for data break on the I/O bus
* MC8S Memory Extension Control, which was needed to support more than 4k [[word]]s of memory
* MM8S Memory Module
* ME8S Memory Extension, holds two MM8S

{{Nav PDP-8}}

[[Category: PDP-8s]]

PDP-8

2019-08-18T17:32:06Z

Nczempin: for the 2 MHz clock, see "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."

''This article is about the first PDP-8, which had that name without a model suffix. For information about PDP-8's in general, see [[PDP-8 family]].''

{{Infobox Machine
| name = PDP-8
| image = PDP-8.jpg
| caption = An original, transistorized PDP-8
| manufacturer = [[Digital Equipment Corporation|DEC]]
| form factor = [[minicomputer]]
| word size = 12 bits
| year introduced = 1965
| year discontinued = 1969
| architecture = [[PDP-8 architecture|PDP-8]]
| physical address = 32k words (requires optional Type 183)
| virtual address = 4k words
| design type = [[clock]]ed random [[logic]]
| clock speed = 2 MHz
| additions per second = 333
| memory speed = 1.5 μseconds
| memory mgmt = bank select
| logic type = [[diode transistor logic|DTL]]
| bus arch = Negative I/O Bus
| predecessor = [[PDP-5]]
| successor = [[PDP-8/I]]
| price = US$18,500

}}

The '''PDP-8''' (now often known as a '''Straight 8'''; the name dates from the late 60's, apparently adopted to allow disambiguation), the first model of the [[PDP-8 family]], was [[Digital Equipment Corporation|DEC]]'s major breakthrough, and now considered the first really successful [[minicomputer]]. It was, by a significant amount, the cheapest computer yet made at the time.

The PDP-8 was constructed with discrete [[transistor]]s, packaged into DEC's [[FLIP CHIP]] technology. It could perform an addition to the [[accumulator]] in 3.0 μseconds, and a 12 by 12 bit multiplication with 24 bit result in 15 μseconds (average; range 9 to 21), using the optional math extension hardware (below).

==Options==

Options included:

* Type 183 Memory Extension Control, which was needed to support more than 4k [[word]]s of memory
* Type 184 Memory Module
* Type 188 Memory Parity
* Type 182 Extended Arithmetic Element, which supported [[hardware]] integer multiplication and division, multi-[[bit]] double-word shifts, and [[normalization]]

== Operating Systems ==

The PDP-8 could run various operating systems including:
*[[OS/8]]
*[[TSS/8]]
*COS-310

== Emulators ==

There are various emulators for PDP-8 systems including:

*[[SIMH]]

== Application software/Simulation software ==

Mention in this video regarding a PDP-8 screen running J.H. Conways game of life:

* [https://www.youtube.com/watch?v=R9Plq-D1gEk Inventing Game of Life - Numberphile]

{{Nav PDP-8}}

[[Category: PDP-8s]]
[[Category: DEC Systems]]

PDP-8

2019-08-18T16:26:35Z

Nczempin: k is small

''This article is about the first PDP-8, which had that name without a model suffix. For information about PDP-8's in general, see [[PDP-8 family]].''

{{Infobox Machine
| name = PDP-8
| image = PDP-8.jpg
| caption = An original, transistorized PDP-8
| manufacturer = [[Digital Equipment Corporation|DEC]]
| form factor = [[minicomputer]]
| word size = 12 bits
| year introduced = 1965
| year discontinued = 1969
| architecture = [[PDP-8 architecture|PDP-8]]
| physical address = 32k words (requires optional Type 183)
| virtual address = 4k words
| design type = [[clock]]ed random [[logic]]
| clock speed = 333 kHz
| memory speed = 1.5 μseconds
| memory mgmt = bank select
| logic type = [[diode transistor logic|DTL]]
| bus arch = Negative I/O Bus
| predecessor = [[PDP-5]]
| successor = [[PDP-8/I]]
| price = US$18,500

}}

The '''PDP-8''' (now often known as a '''Straight 8'''; the name dates from the late 60's, apparently adopted to allow disambiguation), the first model of the [[PDP-8 family]], was [[Digital Equipment Corporation|DEC]]'s major breakthrough, and now considered the first really successful [[minicomputer]]. It was, by a significant amount, the cheapest computer yet made at the time.

The PDP-8 was constructed with discrete [[transistor]]s, packaged into DEC's [[FLIP CHIP]] technology. It could perform an addition to the [[accumulator]] in 3.0 μseconds, and a 12 by 12 bit multiplication with 24 bit result in 15 μseconds (average; range 9 to 21), using the optional math extension hardware (below).

==Options==

Options included:

* Type 183 Memory Extension Control, which was needed to support more than 4k [[word]]s of memory
* Type 184 Memory Module
* Type 188 Memory Parity
* Type 182 Extended Arithmetic Element, which supported [[hardware]] integer multiplication and division, multi-[[bit]] double-word shifts, and [[normalization]]

== Operating Systems ==

The PDP-8 could run various operating systems including:
*[[OS/8]]
*[[TSS/8]]
*COS-310

== Emulators ==

There are various emulators for PDP-8 systems including:

*[[SIMH]]

== Application software/Simulation software ==

Mention in this video regarding a PDP-8 screen running J.H. Conways game of life:

* [https://www.youtube.com/watch?v=R9Plq-D1gEk Inventing Game of Life - Numberphile]

{{Nav PDP-8}}

[[Category: PDP-8s]]
[[Category: DEC Systems]]

User:Nczempin

2019-08-18T16:11:19Z

Nczempin: starting point: link to my user page on the English Wikipedia

[https://en.wikipedia.org/wiki/User:nczempin My Wikipedia page]