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PDP-8/e

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PDP-8/E
PDP-8/E in a rack cabinet at the Computer History Museum (Tomwsulcer, CC0)
Specifications
ManufacturerDigital Equipment Corporation
Type12-bit minicomputer
Released1970[1][2]
Discontinued1978[1]
Intro priceUS$6,500 at introduction[1][2]
CPUTTL processor on three quad modules (M8300, M8310, M8330); 1.2 µs fast and 1.4 µs slow memory cycles[3][1]
Memory4,096 12-bit words of core (MM8-E), up to 32K[3]
Storage—
Display—
Sound—
Expansion20-slot OMNIBUS (10 used by the basic computer), expandable to 60 slots[4]
Power95–130 V or 185–250 V AC, 47–63 Hz; 450 W; H724 or H724A supply[3][5]
Dimensions10.5 × 19 × 24 in[2]
WeightAbout 100 lb, of which the power supply is about 45 lb[2]
OS / Firmware—
PredecessorPDP-8/I, PDP-8/L[1]
SuccessorPDP-8/A[1]

The PDP-8/E is a 12-bit minicomputer introduced by Digital Equipment Corporation in 1970 at US$6,500.[1][2] It replaced the wire-wrapped backplanes of the earlier PDP-8 models with the OMNIBUS, a backplane in which every slot is wired identically, and put the whole processor on three large "quad" modules of TTL logic.[1] Options plug into the same bus as single cards. DEC built the cheaper PDP-8/F and the OEM PDP-8/m around the same processor from 1972, and withdrew all three in 1978 as the PDP-8/A took over.[1][6] Wikipedia calls the PDP-8/E common and well regarded, because so many I/O devices were made for it.[7]

The 8/E, 8/F and 8/M share their processor, memory and options, and DEC's maintenance manual covers all three; they differ in box, front panel and power supply.[4][5] See PDP-8/e Power Supply Guide, PDP-8/e General Maintenance and PDP-8/e Troubleshooting.

Specifications

PDP-8/E technical characteristics (DEC-8E-HMM1A, Table 1-1)
Item Specification
Memory cycle Fast 1.2 µs (fetch, internal IOT, non-autoindex defer); slow 1.4 µs (execute, autoindex defer)
Memory reference instruction 2.6 µs (one fast and one slow cycle)
Word length 12 bits
Memory 4,096 words, up to 32K optional
Mains (processor) 95–130 V, 47–63 Hz, about 6 A; or 185–250 V, 47–63 Hz, about 3 A; 450 W
Operating environment 0 to 55 °C, 10 to 95 % relative humidity, non-condensing

[3]

Hardware

Processor and OMNIBUS

The basic PDP-8/E has eight functional parts: the M8330 timing generator, M8310 register control, M8300 major registers, MM8-E core memory, H724 power supply, M8320 bus loads, M8650 Teletype control and KC8-EA programmer's console, with an M849 RFI shield between memory and the other options.[8] The OMNIBUS has 20 slots, ten of them needed by the basic computer; an OMNIBUS expander adds 20 more inside the box, and an expander box brings the total to 60.[4] Boards that work as a set (the CPU, the EAE, the memory) are joined across their tops by H851 edge connectors.[2] DEC's recommended order puts the console first, the M8330 next to it, and the M8320 bus loads always in the last slot.[9]

Memory

The MM8-E 4K core memory is three boards: G104 sense/inhibit, H220 stack and G227 X/Y drivers. Each further 4K field is another triplet, which needs the M837 (KM8-E) memory extension control.[9][1] The slice level and X/Y current are set at the factory with jumpers, the field number with three jumpers on the G104, and the sense strobe with a six-position switch.[10]

Power supply

The H724 (H724A for 230 V) provides +5 V at 20 A for the logic, −15 V at 8 A and +15 V at 1 A for the memory and bus loads, unregulated +8 V at 2 A for the console lamps, and a 28 V AC centre-tapped winding, brought out as 14 V AC for options.[11][12] It is a linear supply weighing about 45 lb.[2] The KC8-EA programmer's console has incandescent lamps fed from the unregulated +8 V, which is why it cannot be fitted to an 8/F, whose supply has no +8 V output.[11][6] David Gesswein notes that the H724 does not provide enough +5 V for a box full of M-series cards, because DEC assumed most slots would hold memory.[13]

Known problems

  • Electrolytic capacitors in the H724: DEC's own preventive maintenance asks for the supply to be inspected for leaky capacitors and overheated resistors every three months.[14] See PDP-8/e Power Supply Guide.
  • Mismatched boards: early modules with three-digit numbers (M833, M865) were defective in various ways and were replaced by the M8330 and M8650.[1]

See PDP-8/e Troubleshooting.

Documentation

See PDP-8/e Documentation for these and the PDP-8/M and H740 drawing sets.

  • PDP-8/E with its cover off, VCF Berlin 2014 (Morn, CC BY-SA 3.0)
    PDP-8/E with its cover off, VCF Berlin 2014 (Morn, CC BY-SA 3.0)
  • PDP-8/E power supply during restoration (Tony Duell, CC BY 2.0)
    PDP-8/E power supply during restoration (Tony Duell, CC BY 2.0)
  • DEC's component location drawing of the H724
    DEC's component location drawing of the H724

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Douglas W. Jones, "What is a PDP-8/E?", PDP-8 Summary of Models and Options (comp.sys.dec FAQ), faqs.org. Introduction 1970, withdrawal 1978, US$6,500, three-board CPU on the OMNIBUS, MM8-E triplets, early defective modules, replacement by the PDP-8/A.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 David Gesswein, "PDP-8/E and PDP-8/M Computer Information", pdp8online.com. Introduction 1970 at US$6,500, H851 connectors, size and weight, power supply weight.
  3. ↑ 3.0 3.1 3.2 3.3 Digital Equipment Corporation, PDP-8/E, PDP-8/F, PDP-8/M Maintenance Manual, Volume 1: Processor, DEC-8E-HMM1A-D-D, September 1973, pp. 1-7 to 1-8, Table 1-1 (File:PDP-8E Maintenance Manual Volume 1 (DEC-8E-HMM1A-D-D).pdf).
  4. ↑ 4.0 4.1 4.2 DEC, DEC-8E-HMM1A-D-D, p. 1-2, "Description".
  5. ↑ 5.0 5.1 DEC, DEC-8E-HMM1A-D-D, p. 3-172, section 8, power supplies (H724 or H724A for 230 V).
  6. ↑ 6.0 6.1 Douglas W. Jones, "What is a PDP-8/F?", faqs.org. PDP-8/F and 8/M introduced 1972, withdrawn 1978; the 8/E front panel needs the +8 V lamp supply.
  7. ↑ "PDP-8", Wikipedia, en.wikipedia.org/wiki/PDP-8.
  8. ↑ DEC, DEC-8E-HMM1A-D-D, pp. 3-2 to 3-4, "PDP-8/E Basic System".
  9. ↑ 9.0 9.1 DEC, DEC-8E-HMM1A-D-D, pp. 2-6 to 2-7, Tables 2-2 and 2-3, jumpers and recommended module order.
  10. ↑ DEC, DEC-8E-HMM1A-D-D, pp. 4-20 to 4-22, Table 4-6 and sections 4.7.3 to 4.7.9, memory circuit variables.
  11. ↑ 11.0 11.1 DEC, DEC-8E-HMM1A-D-D, pp. 3-172 to 3-176, section 3.47, PDP-8/E power supply.
  12. ↑ DEC, DEC-8E-HMM1A-D-D, p. 4-23, Table 4-7, H724 power supply parameters.
  13. ↑ David Gesswein, "PDP-8 h724 Power Supply Information", pdp8online.com.
  14. ↑ DEC, DEC-8E-HMM1A-D-D, pp. 4-5 to 4-6, Table 4-2, processor preventive maintenance schedule.

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