Josh: New page: PDP-8/E and 8/M from DEC maintenance manual, IPB and drawings

2026-10-02T01:24:25Z

New page: PDP-8/E and 8/M from DEC maintenance manual, IPB and drawings

New page

{{Infobox computer
| name = PDP-8/M
| image = [[File:DEC PDP-8M (Dave Ruske).jpg|260px|frameless]]
| caption = PDP-8/M with the KC8-ML programmer's console (Dave Ruske, CC BY 2.0)
| manufacturer = Digital Equipment Corporation
| type = 12-bit minicomputer (OEM version of the PDP-8/F)
| release_date = 1972<ref name="faq8m" />
| discontinued = 1978<ref name="faq8m" />
| cpu = PDP-8/E processor (M8300, M8310, M8330)<ref name="faq8m" /><ref name="mm5" />
| memory = MM8-E core, 4K per G104/H220/G227 set<ref name="mm5" />
| power = H740 switching supply: 90–135 or 180–270 V AC, 47–63 Hz, 325 W at full load<ref name="spec" />
| expansion = OMNIBUS; expandable by 40 slots with an expander box<ref name="mm12" />
| predecessor = PDP-8/E<ref name="faq8f" />
| successor = PDP-8/A<ref name="faq8f" />
}}
The '''PDP-8/M''' is the OEM version of Digital Equipment Corporation's PDP-8/F, introduced in 1972 for companies that built the computer into their own systems.<ref name="faq8m" /> Behind the front panel it is a PDP-8/E: the same OMNIBUS modules, CPU and core memory, in a shorter box with a smaller H740 switching power supply in place of the 8/E's H724 linear supply.<ref name="faq8f" /><ref name="mm8" /> The H740 was the first switching supply in the PDP-8 family.<ref name="faq8f" /> DEC withdrew the 8/F and 8/M in 1978, when the PDP-8/A 800 offered similar expansion for less.<ref name="faq8f" />

The 8/M's standard front panel is a minimal operator's panel, so a machine needs either the KP8-E power-fail and auto-restart option or the MI8-E hardware bootstrap loader to start a program. The KC8-ML programmer's console with lamps and switches was an option; with it fitted, an 8/M differs from an 8/F only in the front panel artwork, colour scheme and labels.<ref name="faq8m" /><ref name="mm12" /> David Gesswein notes that 8/Ms often lacked the full programmer's console; his has one, as does the machine pictured here.<ref name="djg" />

== Specifications ==
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ '''H740 power supply ratings (DEC specification 5409728-0-8)'''
! Output !! Load range !! Notes
|-
| +5 V || 0–20 A static at 50 °C (0–17 A at 60 °C) || Switching regulator; crowbar at 5.7–6.8 V blows the fuse
|-
| −15 V || 0–5, 0–7 or 0–8 A by regulator board revision || Switching regulator; crowbar at 17.5–20.5 V
|-
| +15 V || 0–1 A || Linear; current limit 1.3–1.7 A
|-
| Mains input || 90–135 V or 180–270 V, 47–63 Hz, 5 or 2.5 A || 325 W at full load; 25 ms hold-up at low line and full load
|}
<ref name="spec" />
The processor, memory, cycle times and instruction set are those of the [[PDP-8/e]].<ref name="faq8f" /><ref name="mm5" />

== Hardware ==
=== Front panels ===
The KC8-ML has light-emitting diodes in place of the 8/E's incandescent lamps. The H740 has no +8 V lamp supply, so an 8/E KC8-EA console cannot be used on an 8/F or 8/M, although the LED console fits an 8/E.<ref name="faq8f" /><ref name="mm5" /> With the introduction of the M8330 timing board, DEC required it to sit next to the console.<ref name="faq8f" />

=== Power supply ===
The H740 transforms the mains to 28 V AC, centre-tapped, and derives every DC output from that. The +5 V and −15 V regulators are switching circuits running at about 10 kHz; the +15 V regulator is linear.<ref name="mm348" /><ref name="djgh724" /> A thermostat on the regulator board's heat sink cuts the transformer and fan power when it overheats.<ref name="mm348" /><ref name="spec" /> The original 8/F box had a defective power supply, corrected in a revised, slightly larger box, and the KP8-E power-fail option as first sold did not work with the 8/F supply.<ref name="faq8f" /> David Gesswein also notes that the first H740s had problems and later ones were better.<ref name="djgh724" /> See [[PDP-8/m Capacitor Replacement Guide]] and [[PDP-8/m Troubleshooting]].

== Documentation ==
* ''PDP-8/E, PDP-8/F, PDP-8/M Maintenance Manual, Volume 1'', DEC-8E-HMM1A-D-D, 1973: [[:File:PDP-8E Maintenance Manual Volume 1 (DEC-8E-HMM1A-D-D).pdf]]
* ''PDP-8/M Engineering Drawings'', November 1973: [[:File:PDP-8M Engineering Drawings (November 1973).pdf]]
* ''H740 Power Supply Engineering Drawings'', revision H: [[:File:H740 Power Supply Engineering Drawings (Rev H, 1974).pdf]]
See [[PDP-8/e Documentation]].

== Gallery ==
<gallery mode="packed" heights="200">
File:DEC PDP-8M with paper tape reader (VCFB 2019).jpg|PDP-8/M with a paper tape reader at VCF Berlin 2019 (stiefkind, CC0)
File:DEC H740 regulator board 5409728 assembly drawing.png|DEC assembly drawing of the H740 regulator board
</gallery>

== Related pages ==
* [[PDP-8/m General Maintenance]]
* [[PDP-8/m Troubleshooting]]
* [[PDP-8/m Capacitor Replacement Guide]]
* [[PDP-8/e]]
* [[PDP-8/e Documentation]]

== References ==
<references>
<ref name="faq8m">Douglas W. Jones, "What is a PDP-8/M?", ''PDP-8 Summary of Models and Options'' (comp.sys.dec FAQ), [http://www.faqs.org/faqs/dec-faq/pdp8-models/section-10.html faqs.org]. Introduced 1972, withdrawn 1978, OEM packaging of the 8/F, minimal front panel requiring KP8-E or MI8-E, KC8-M option.</ref>
<ref name="faq8f">Douglas W. Jones, "What is a PDP-8/F?", [http://www.faqs.org/faqs/dec-faq/pdp8-models/section-9.html faqs.org]. First switching supply in the family, LED front panel and the +8 V restriction, M8330 placement, defective original supply and revised box, KP8-E incompatibility, replacement by the PDP-8/A 800.</ref>
<ref name="djg">David Gesswein, "PDP-8/E and PDP-8/M Computer Information", [https://www.pdp8online.com/pdp8em/pdp8em.shtml pdp8online.com]. The 8/M was an OEM version of the 8/F and frequently lacked the full front panel.</ref>
<ref name="djgh724">David Gesswein, "PDP-8 h724 Power Supply Information", [https://www.pdp8online.com/pdp8em/h724.shtml pdp8online.com]. H740 switching at about 10 kHz; early H740s had problems.</ref>
<ref name="mm12">Digital Equipment Corporation, ''PDP-8/E, PDP-8/F, PDP-8/M Maintenance Manual, Volume 1: Processor'', DEC-8E-HMM1A-D-D, September 1973, p. 1-2 ([[:File:PDP-8E Maintenance Manual Volume 1 (DEC-8E-HMM1A-D-D).pdf]]). KC8-M operator's panel; expansion by 40 slots.</ref>
<ref name="mm8">DEC, DEC-8E-HMM1A-D-D, p. 3-172, section 8: the 8/F and 8/M use the H740.</ref>
<ref name="mm348">DEC, DEC-8E-HMM1A-D-D, pp. 3-177 to 3-181, section 3.48, PDP-8/F and PDP-8/M power supply.</ref>
<ref name="mm5">DEC, DEC-8E-HMM1A-D-D, pp. 5-5 to 5-6, Tables 5-5 and 5-6, PDP-8/F and PDP-8/M first-level spares (M8300, M8310, M8330, G104, G227, LEDs, regulator board 54-09728).</ref>
<ref name="spec">Digital Equipment Corporation, engineering specification SP-5409728-0-8, "Power Supply Specification – H740", sheets 8 to 13, in ''H740 Power Supply Engineering Drawings'', revision H ([[:File:H740 Power Supply Engineering Drawings (Rev H, 1974).pdf]]), PDF pp. 16 to 19.</ref>
</references>

[[Category:Digital Equipment Corporation]]

PDP-8/m - Revision history

Josh: New page: PDP-8/E and 8/M from DEC maintenance manual, IPB and drawings