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- From: jones@cs.uiowa.edu (Douglas W. Jones)
- Newsgroups: alt.sys.pdp8,alt.answers,news.answers
- Subject: PDP-8 Summary of Models and Options (posted every other month)
- Followup-To: alt.sys.pdp8
- Date: 8 Jun 2001 08:08:08 GMT
- Organization: Computer Science, University of Iowa, Iowa City, Iowa, USA
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- Summary: Descriptions of all models of the DEC PDP-8 computer.
- Those posting to alt.sys.pdp8 should read this.
- Keywords: FAQ DEC PDP 8
- Xref: senator-bedfellow.mit.edu alt.sys.pdp8:6521 alt.answers:55887 news.answers:208796
-
- Archive-name: dec-faq/pdp8-models
- Last-modified: Oct 1, 2000
-
- Frequently Asked Questions about DEC PDP-8 models and options.
-
- By Douglas Jones, jones@cs.uiowa.edu
- (with help from many folks)
-
- Sites known to carry reasonably current FTPable copies of this file:
-
- ftp://rtfm.mit.edu/pub/usenet/alt.sys.pdp8
- ftp://ftp.uu.net/usenet/news.answers/dec-faq
- ftp://src.doc.ic.ac.uk:/pub/usenet/news.answers/alt.sys.pdp8
-
- Reasonably current automatic translations of this document to HTML format
- for the World Wide Web are available from:
-
- http://www.faqs.org/faqs/dec-faq/
- http://www.cs.ruu.nl/wais/html/na-dir/dec-faq/.html
-
- An obsolete version of this file is available on the Walnut Creek USENET
- FAQ CDROM; another version will be published as part of the FAQbook by
- Pamela Greene et al.
-
- This posting conforms to RFC1153 USENET digest format (with exceptions due
- to the fact that it is not really a digest).
-
- The purpose of this document is to supplement the material in the primary
- "Frequently Asked Questions about the PDP-8" file with more detailed
- information about the hardware and options of the different models of the
- PDP-8 sold by DEC.
-
- Although this document is something of a history of the DEC PDP-8 family,
- the primary purpose of this document is as a guide and general outline to
- the PDP-8 models and options likely to be encountered by those involved
- in collecting and restoring such systems.
-
- Contents:
-
- What is a PDP-5?
- What is a PDP-8?
- What is a LINC-8?
- What is a PDP-8/S?
- What is a PDP-8/I?
- What is a PDP-8/L?
- What is a PDP-12?
- What is a PDP-8/E?
- What is a PDP-8/F?
- What is a PDP-8/M?
- What is a PDP-8/A?
- What is a VT78?
- What is a DECmate I?
- What is a DECmate II?
- What is a DECmate III?
- What is a DECmate III+?
-
- ----------------------------------------------------------------------
-
- Subject: What is a PDP-5?
-
- Date of introduction: Aug 11, 1963, unveiled at WESCON.
- Date of withdrawal: early 1967.
- Total production run: 116.
- Price: $27,000
-
- Technology: The PDP-5 was built with DEC System Modules, the original
- line of transistorized logic modules sold by DEC. The supply
- voltages were +10 and -15 volts, with logic levels of -3 (logic 1)
- and 0 (logic 0). Logic was packaged on boards that were about
- 4.75 inches high with each card mounted in a metal frame with a
- 22 pin edge connector.
-
- Input output devices were connected to the daisy-chained I/O bus
- using military-style armored cables and connectors. Use of
- toggle switches (as opposed to slide switches) on the front
- panel was another vestige of military-style design.
-
- Reason for introduction: This machine was inspired by the success of
- the CDC-160, Seymour Cray's 12 bit minicomputer, and by the
- success of the LINC, a machine that was built by DEC customers
- out of System modules. These demonstrated that there was a
- market for a small inexpensive computer, and from the start,
- DEC's advertisements were aimed at this market. "Now you can
- own the PDP-5 computer for what a core memory alone used to
- cost: $27,000", ran one 1964 ad.
-
- Ken Olson has stated that the PDP-5 was not originally meant to
- be a computer; it was designed for a company that wanted an
- automatic controller for some industrial work. He told them
- they could make a small programmable controller instead of the
- hardwired machine they were asking for, and since they weren't
- entirely certain of the control equations they wanted to run, they
- accepted the idea. The result was the PDP-5.
-
- Reason for withdrawal: The PDP-8 outperformed the PDP-5, and did so for
- a lower price.
-
- Compatability: The core of the PDP-8 instruction set is present, but
- memory location zero is the program counter, and interrupts are
- handled differently. The Group 1 OPR rotate instructions cannot
- be combined with IAC or CMA; this limits the ability of the
- PDP-5 to support code from later models.
-
- The machine does not support 3 cycle data-break (DMA transfers using
- memory to hold buffer address and word-count information), so
- many later PDP-8 peripherals cannot be used on the PDP-5. In
- addition, DMA transfers are not allowed outside the program's
- current 4K data field, severely limiting software compatability
- on systems with over 4K of memory where either interrupts or
- software initiated changes to the data field during a transfer
- would cause chaos.
-
- Standard configuration: CPU with 1K or 4K of memory (2K and 3K versions
- were not available).
-
- Peripherals:
- An extended arithmetic element (EAE) was available; this was an
- I/O device, using IOT instructions to evoke EAE operations. As
- a result, it was not compatable with the later PDP-8 EAEs. In
- addition, machines with the EAE option had a different front
- panel from those without.
-
- The type 552 DECtape control and type 555 dual DECtape transports
- were originally developed for the PDP-5 and contemporaneous DEC
- systems such as the PDP-6.
-
- After the PDP-8 was introduced, DEC offered a bus converter that
- allowed the PDP-5 to support standard PDP-8 negibus ueripherals,
- so long as they avoided using 3-cycle data break transfers. The
- standard 804 PDP-8 expander box was frequently sold as an
- upgrade to PDP-5 systems.
-
- Survival: A small number of PDP-5 systems survive, at least one in near
- operational condition!
-
- ------------------------------
-
- Subject: What is a PDP-8?
-
- Date of introduction: 1965 (Unveiled March 22, in New York).
- Date of withdrawal: 1968.
- Total production run: 1450.
- Also known as:
- Classic PDP-8 (to point out lack of a model suffix)
- Straight-8 (Again, points out the lack of a model suffix)
- PCP-88, an OEM label, used by Foxboro Corporation.
- AN/GYK-6, (Army-Navy Ground-based (Y)data-processing Komputer 6)
- Price: $18,000
-
- Technology: Mostly standard DEC R-series logic modules; these were
- originally discrete component transistor logic, but around the
- time the PDP-8 was introduced, DEC introduced the Flip Chip, a
- hybrid diode/resistor "integrated circuit" on a ceramic substrate.
- These could directly replace some of the discrete components on
- some logic modules, and DEC quickly began to refer to all R-series
- modules as flip-chip modules; they even advertised the PDP-8 as
- an integrated circuit computer. A typical flip-chip module, the
- R111, had three 2-input nand gates and cost $14, with no price
- change from 1965 to 1970. Some special dual height R-series
- modules were designed specifically for the PDP-8.
-
- S and B-series logic modules were also used; these are similar
- to their R-series cousins, but with different speed/fanout
- tradeoffs in their design. Some logic modules have trimmers
- that must be tuned to the context, making replacement of such
- modules more complex than simply swapping boards.
-
- As with the system modules used in the PDP-5, the supply
- voltages were +10 and -15 volts and the logic levels were -3
- (logic 1) and 0 (logic 0). Logic was packaged on boards that
- were 2.5 inches wide by 5 inches long. The card edge connector
- had 18 contacts on 1/8 inch centers. Some double height cards
- were used; these had two card edge connectors and were 5 1/8
- inches high. Machine wrapped wire-wrap technology was used on
- the backplane using 24-gauge wire.
-
- The "negibus" or negative logic I/O bus used -3 and 0 volt logic
- levels in 92 ohm coaxial cable, with 9 coaxial cables bundled
- per connector card and 6 bundles making up the basic bus. 5
- (later 4) more bundles were required to support data-break (DMA)
- transfers. The total bus length was limited to 50 feet, and bus
- termination was generally kluged in with 100 ohm resistors
- clipped or wrapped into the backplane, although a bus terminator
- card was sometimes used. Some time after the first year of
- production, flat ribbon cable made of multiple coaxial cables
- was used, and later still, shielded flat stripline cable was used
- (but this cut the allowed bus length by a factor of two).
-
- Core memory was used, originally made by FERROXCUBE, with a 1.5
- microsecond cycle time, giving the machine an add time of 3
- microseconds. 4K of core occupied an aluminum box 6 inches on a
- side and needed numerous auxiliary flip-chips and for support,
- as well as an array of boards from the core vendor. It is worth
- noting that the PDP-8 was about as fast as was practical with the
- logic technology used; only by using tricks like memory
- interleaving or pipelining could the machine have been made much
- faster.
-
- Reason for introduction: This machine was inspired by the success of
- the PDP-5 and by the realization that, with their new Flip-Chip
- technology, DEC could make a table-top computer that could be
- powered by a single standard wall outlet; of course, adding any
- peripherals quickly increased the power requirement!
-
- Reason for withdrawal: The PDP-8/I was less expensive, and after
- initial production difficulties, it equalled the performance of
- the PDP-8.
-
- Compatability: This machine defines the core of the PDP-8 instruction
- set, but with restrictions that were lifted on later machines.
- The Group 1 OPR instruction IAC cannot be combined with any of
- the rotate instructions. If RAR and RAL or RTR and RTL are
- combined, the results are unpredictable (simultaneous set and
- reset of bits of AC results in metastable behavior). The IOT 0
- instruction was used for the internal type 189 ADC, and not for
- the later CAF (clear all flags) instruction. As a result, if
- the ADC option was not present, IOT 6004 (or microcoded
- variants) would hang the machine.
-
- The SWP instruction (exchange AC and MQ) never works, even if
- the extended arithmetic element is present. This works on later
- models when the EAE is present, although it was only documented
- with the introduction of the PDP-8/E. Finally, the EAE lacks
- the SCL (shift count load) instruction that is present on later
- models.
-
- On machines with 8K or more, an attempt to change the data field
- to a non-existant field caused a bizarre double-indirect and
- skip instruction execution that must be accounted for in memory
- diagnostics.
-
- Standard configuration: The PDP-8 was sold as a CPU with 4K of memory,
- a 110 baud current loop teletype interface and an ASR 33 Teletype.
- In addition, the standard in-cabinet logic includes support for
- the full negibus interface, including data-break (DMA) transfers.
-
- Both a rack-mount model with rosewood trim and an elegant
- plexiglass enclosed table-top configuration were standard. Under
- the skin, the basic machine occupies a volume 33 inches high by
- 19 inches wide by 22 inches deep. The two halves of the backplane
- are mounted vertically, like the covers of a book, with the
- spine in back and circuit modules inserted from the two sides.
- Sliding the CPU out of the relay rack or removing the plexiglass
- covers allows the backplane to swung open to access the wires-wrap.
-
- Expandability: In-cabinet options include the type 182 extended
- arithmetic element (EAE) ($3,500), the type 183 memory extension
- control subsystem ($3000), and the type 189 low performance
- analog to digital converter ($1450). Prewired backplane slots
- were reserved for all of these, as well as the optional type 129
- data channel multiplexor ($2700).
-
- Expansion beyond 4K of memory requires rack mounting space (at
- $690 per CAB-8 rack). Each type 184 memory module adds a 4K
- field of memory ($10,000), seven modules may be added. The
- rack-mount CPU occupied a large part of one rack, allowing room
- for a single memory expansion module below the CPU; generally,
- a second rack was needed for added peripherals or memory.
-
- At the end of the production run, some PDP-8 systems were sold
- with PDP-8/I memory, allowing room for an additional 4K without
- need for an expansion chassis. These nonstandard machines were
- very difficult to maintain!
-
- Peripherals: At the time of introduction, the following negibus
- peripherals were offered.
-
- -- Type 750 high speed paper tape reader and control ($3500).
- -- Type 75A high speed paper tape punch and control ($4000).
- -- Type 138 analog to digital converter ($4500).
- -- Type 139 analog multiplexor ($3300).
- -- Type 30N precision CRT display ($13,400).
- -- Type 34B oscilloscope display ($3600).
- -- Type 370 high speed light pen ($1625)
- -- Type 350 incremental (CalComp) plotter and control ($8,900 up).
- -- Type 451 card reader and control ($14,900).
- -- Type 451B fast card reader and control ($25,600).
- -- Type 450 card punch control for IBM Type 523 punch.
- -- Type 64 (later 645) Mohawk line printer and control ($28,900).
- -- Type 250 (RM08) serial magnetic drum (256K words for $43,600).
- -- Type 552 DECtape control (for type 555 DECtape drives, $9500).
- -- Type 555 dual DECtape transport, $7400).
- -- Type 57A magnetic tape control with IBM type 729 drive ($15,200).
- -- Type 580 magnetic tape system with one transport ($19,700).
-
- By 1966, the following peripherals had been added to the line:
-
- -- Type AA01A three-channel digital to analog converter.
- -- Type CR01C card reader control.
- -- Type TC01 DECtape control for up to 8 TU55 transports.
- -- Type 251 drum (8-256 tracks, 8 sectors/track, 128 words/sector).
- -- Type 645 line printer control.
- -- Type 680 data communications system (allows 64 teletypes).
-
- By 1967, the following peripherals had been added to the line:
-
- -- Type AF01 analog to digital converter and multiplexor.
- -- Type AX08 parallel digital input port.
- -- Type 338 Programmed Buffered Display (vector graphics).
-
- By 1968, the following new peripheral had been added:
-
- -- Type DF32 fixed head disk system (32K to 256K words).
- -- Type BE01 OEM version of the TC01 (no blinking lights).
- -- Type BE03 dual TU55 drive for the TC01 or BE01.
-
- Finally, as DEC abandoned the negibus, they introduced the
- DW08B negibus to posibus converter so newer posibus
- peripherals could be used on older negibus machines, and the
- DW08A posibus to negibus converter to allow use of old
- peripherals on new machines.
-
- Survival: Many classic PDP-8 systems survive to this day in working
- condition.
-
- ------------------------------
-
- Subject: What is a LINC-8?
-
- Date of introduction: 1966 (during or before March).
- Date of withdrawal: 1969
- Total production run: 142.
- Price: $38,500
-
- Technology: DEC Flip Chip modules, as in the PDP-8, with a LINC CPU
- partially reimplemented in Flip Chips and partially emulated
- with PDP-8 instructions. (The original LINC was built from
- the same System Modules used in the PDP-5.)
-
- Compatability: The PDP-8 part of the machine was identical to the PDP-8.
-
- Reason for withdrawal: The PDP-12 accomplished the same goals at a lower
- cost.
-
- Standard configuration: The combined PDP-8/LINC CPU, plus 4K of memory
- was central to the system. The set of peripherals bundled with
- the machine was impressive:
-
- -- An ASR 33 Teletype modified for the LINC character set.
- -- Two LINCtape drives.
- -- 8 analog to digital converter channels with knob inputs.
- -- Another 8 ADC channels with jack inputs.
- -- 6 programmable relay outputs, good up to 60 Hz.
- -- 1 Tektronix 560 oscilliscope, somewhat modified.
-
- The X and Y axis control for the scope came from DACs attached
- to the LINC's AC and MB registers, respectively.
-
- Expandability:
-
- In addition to standard PDP-8 peripherals, up to 3 additional
- pairs of LINCtape drives could be added, for a total of 8 drives.
- The design of the type 555 dual DECtape transport was based on
- that of the LINCtape drive.
-
- Up to 2 additional ranks of 8 ADC channels could be added.
-
- Remote oscilliscope could be added.
-
- Survival: A few LINC-8 systems are in operable condition today.
-
- ------------------------------
-
- Subject: What is a PDP-8/S?
-
- Date of introduction: 1966 (Unveiled, Aug 23, WESCON, Los Angeles).
- Date of withdrawal: 1970.
- Total production run: 1024, or over 1500
- The first figure is from Computers and Automation, based on figures
- released by the manufacturer. The second figure is based on memory
- of the first-year production run. We need to look at the serial
- numbers on surviving machines to pin this down!
- Price: $10,000
-
- Technology: DEC Flip Chip modules and core memory, as in the PDP-8.
- Unlike the PDP-8, the PDP-8/S memory module was mounted between
- a pair of quad-height single-width boards that plugged into the
- standard flip-chip sockets (this was sold separately as the H201
- core memory unit, at $2000 for 4K by 13 bits). It is noteworthy
- that the prototype machine was built using Digital Logic Laboratory
- H901 plugboards and patchcords, based entirely on off-the-shelf
- modules. Another new feature of the PDP-8 was its use of a single
- internal bus within the machine for all register transfers. This
- was, of course, bit serial, but the idea formed the basis for
- the DEC UNIBUS and OMNIBUS and essentially all later bus-oriented
- CPU designs.
-
- Reason for introduction: This machine was developed as a successful
- exercise in minimizing the cost of the machine, in response to
- a complaint by Ken Olson that the company hadn't gotten the
- price of the PDP-8 down any further, and the vision that someday,
- people ought to be able to buy a desktop PDP-8 for under $10,000.
- The result was the least expensive general purpose computer ever
- made with second generation (discrete transistor) technology,
- and it was one of the smallest such machines to be mass produced
- (a number of smaller machines were made for aerospace
- applications). It was also incredibly slow, with a 36
- microsecond add time, and some instructions taking as much as 78
- microseconds, even though the internal clock ran faster than
- that of the original PDP-8! By 1967, DEC took the then unusual
- step of offering this machine for off the shelf delivery, with
- one machine stocked in each field office available for retail
- sale.
-
- Reason for withdrawal: The PDP-8/L vastly outperformed the PDP-8/S, and
- and it did so at a lower price.
-
- Compatability: The core of the PDP-8 instruction set is present, but
- there are a sufficient number of incompatabilities that, as with
- the PDP-5, many otherwise portable "family of 8" programs will
- not run on the PDP-8/S. Perhaps the worst incompatability is
- that the Group 1 OPR instruction CMA cannot be combined with any
- of the rotate instructions; as with the PDP-8, IAC also cannot
- be combined with rotate.
-
- Standard configuration: CPU with 4K of memory, plus PT08 110 baud current
- loop teletype interface and teletype. Both a rack-mount and
- table-top versions were sold (both 9" high by 19" wide by 20"?
- deep). The rack mount version included slides so it could be
- pulled out for maintenance.
-
- Expandability: The CPU supported the standard PDP-8 negibus, but I/O
- bandwidth was 1/5 that of the PDP-8. Thus, most, but not all
- PDP-8 peripherals could be used. A few DEC peripherals such as
- the DF32 came with special options such as interleaving to slow
- them down for compatability with the PDP-8/S. The speed problems
- were such that there was never any way to attach DECtape to this
- machine.
-
- Survival: Because they were so slow, PDP-8/S systems were quickly
- discarded as newer machines became available for comparable prices;
- thus, they are less common today than the Classic PDP-8, even
- though comparable numbers were made. A few survive in working
- condition.
-
- ------------------------------
-
- Subject: What is a PDP-8/I?
-
- Date of introduction: 1968 (Announced before December '67)
- Date of withdrawal: 1971.
- Total production run: 3698.
-
- Technology: DEC M-series logic modules, called M-series flip-chips
- as the term flip-chip was applied to the module format instead
- of to DEC's hybrid integrated circuits. M-series modules used
- TTL chips, with a +5 volt supply, packaged on the same board
- format used with the original flip-chips, but with double-sided
- card-edge connectors (36 contacts instead of 18). Modules were
- limited to typically 4 SSI ICs each. The M113, a typical
- M-series module, had 10 2-input nand gates and cost $23 in 1967
- (the price fell to $18 in 1970). Wire-wrapped backplanes used
- 30-gauge wire.
-
- The PDP-8/I, as originally sold, supported the then-standard
- PDP-8 negibus. 4K words of core were packaged in a 1 inch thick
- module made of 5 rigidly connected 5 by 5 inch two-sided printed
- circuit boards. Connectors and support electronics occupied an
- additional 32 backplane slots.
-
- Nominally, the core memory (which, curiously, used a negative
- logic interface!) was supposed to run at a 1.5 microsecond cycle
- time, but many early PDP-8/I systems were delivered running at a
- slower rate because of memory quality problems. DEC went through
- many vendors in the search for good memory! The memory interface
- was asynchronous, allowing the CPU to delay for slow memory. DEC
- continued to make the classic PDP-8 until the problems with
- memory speed were solved.
-
- Reason for introduction: This machine was developed in response to the
- introduction of DIP component packaging of TTL integrated
- circuits. This allowed a machine of about the same performance
- as the original PDP-8 to fit in about half the volume and sell
- for a lower price.
-
- Reason for withdrawal: The PDP-8/E made slight performance improvements
- while undercutting the price of the PDP-8/I.
-
- Compatability: The core of the PDP-8 instruction set is present, and
- unlike the original PDP-8, IAC can be combined with rotate in a
- single microcoded Group 1 OPR instruction. Combined RAR and RAL
- or RTR and RTL produce the logical and of the expected results
- from each of the combined shifts.
-
- If the extended arithmetic element is present, the SWP (exchange
- AC and MQ) instruction works, but this was not documented.
-
- On large memory configurations, memory fetches from a nonexistant
- memory field take about 30 microseconds (waiting for a bus
- timeout) and then they return either 0000 or 7777 depending on
- the memory configuration and the field that was addressed.
-
- A front panel bug prevented continue after load-address without
- first clearing the machine.
-
- Standard configuration: CPU with 4K of memory, plus 110 baud current
- loop teletype interface. Pedestal, table-top and rack-mount
- versions were made. The pedestal mounted version was futuristic
- looking; the table-top version split the pedistal, with the CPU
- on the table and the power supply (the base of the pedistal) on
- the floor beside the table. The standard rack-mounted version
- had the power supply bolted to the right side of the rack while
- the CPU, mounted on slides, slid out of the left side of the rack.
-
- Expandability: 4K of memory could be added internally, and additional
- memory could be added externally using a rack-mounted MM8I memory
- expansion module for each 4K or 8K addition over 8K.
-
- The backplane of the PDP-8/I was prewired to hold a Calcomp
- plotter interface, with the adjacent backplane slot reserved
- for the cable connection to the plotter. There may be other
- built-in options.
-
- Initially, the CPU was sold with bus drivers for the PDP-8
- negibus, allowing this machine to support all older DEC
- peripherals, but later machines were sold with posibus interfaces,
- and many older machines were converted in the field.
-
- A posibus to negibus converter, the DW08A, allowed use of all
- older PDP-8 peripherals, with small modifications. The change
- from negibus to posibus during the period of PDP-8/I production
- leads to confusion because surviving CPUs and peripherals may
- have any of three I/O bus configurations: Negibus, early posibus,
- or final posibus. The early posibus used the same connectors
- and cables as the negibus, with only 9 conductors per connector,
- while the final posibus used both sides of the connector paddles
- for 18 bus lines per connector. Y-shaped cables for converting
- from one physical bus layout to the other were available. To
- add to this confusion, some negibus PDP-8/I systems were rewired
- to use 18 conductor posibus cables with negative logic!
-
- Eventually, an add-on box was sold that allowed PDP-8/E (OMNIBUS)
- memory to be added to a PDP-8/I. Additionally, Fabritek sold a
- 24K memory box for the 8/I and PDP-12.
-
- Survival: Many PDP-8/I systems are in operating condition, some still
- performing in their original applications!
-
- ------------------------------
-
- Subject: What is a PDP-8/L?
-
- Date of introduction: 1968 (Announced before August '68)
- Date of withdrawal: 1971.
- Total production run: 3902.
- Price: $8,500
-
- Technology: DEC M-series flip Chip modules, as in the PDP-8/I, with the
- same core memory as the 8/I, but with a memory cycle cycle of 1.6
- microseconds to avoid the speed problems that plagued early -8/I
- systems.
-
- The positive I/O bus, or posibus, was a 100 ohm bus clamped
- between 0 and 3 volts with TTL drivers and receivers. This was
- packaged with 18 signal lines per 2-sided interconnect cable,
- using double-sided shielded mylar ribbon cable in most cases.
- Electrically, coaxial cable could be used, but the slots in the
- CPU box were too small for this.
-
- Reason for introduction: This machine was developed as a moderately
- successful exercise using M-series logic to produce a lower cost
- but moderately fast machine. The idea was to cut costs by
- limiting provisions for expansion.
-
- Reason for withdrawal: The PDP-8/E made performance improvements while
- slightly undercutting the price of the PDP-8/L.
-
- Compatability: The core of the PDP-8 instruction set is present, but
- all Group 3 OPR instructions are no-ops, even the Group 3 version
- of the CLA instruction. This is because there was no provision
- made for adding an EAE to this machine. Microcoding RAR and RAL
- together works as in the PDP-8/I. Finally, a new front panel
- feature was added, the protect switch. When thrown, this makes
- the last page of the last field of memory read-only (to protect
- your bootstrap code).
-
- The instruction to change the data field on an 8/L becomes a
- no-op when the destination data field is non-existant; on all
- other machines, attempts to address non-existant fields are
- possible. One option for expanding the 8/L was to add a box that
- allowed 8/E memory modules to be added to the 8/L; when this
- was done, access to nonexistant data fields becomes possible and
- always returns 0000 on read.
-
- Standard configuration: A CPU with 4K of memory, plus 110 baud current
- loop teletype interface was standard. Both rack-mount and
- table-top versions were sold (both 9" high by 19" wide by 21"
- deep). The backplane was on top, with modules plugged in from
- the bottom. The rack-mount version could be slid out for
- maintenance.
-
- Expandability: The CPU supported a new bus standard, the PDP-8 posibus.
- There is little space for in-box peripherals, but an expander
- box with the same volume as the CPU was available, the BA08A;
- this was prewired to hold an additional 4K of memory and to
- support in-box peripheral interfaces for such devices as a
- Calcomp plotter interface, a card-reader interface, a 4 line
- asynch terminal interface, a real-time clock, and more.
-
- DEC eventually offered the BM12L, an 8K expansion box that is
- essentially the same as the MM8I, but using positive logic and
- thus incompatable with the -8/I and -12. This allowed a total
- memory of 12K on a PDP-8/L. This contains precisely the modules
- needed to upgrade a 4K PDP-8/I or PDP-12 to an 8K machine, or to
- populate an MM8I box to add 8K of additional memory to an 8/I or
- PDP-12.
-
- Finally, DEC eventually offered a box allowing PDP-8/E (OMNIBUS)
- memory to be used with the PDP-8/L. PDP-8/L configurations with
- over 8K of memory were awkward because the front panel only
- showed one bit of the extended memory address. As a result,
- extra lights and switches for the additional bits of the memory
- address were mounted on the front of the memory expander boxes
- for the large configurations.
-
- A variety of posibus peripherals were introduced, most of which
- were built with the option of negibus interface logic (the -P
- and -N suffixes on these new peripherals indicated which was
- which). Many early PDP-8/L systems were sold with DW08A bus
- level converters to run old negibus peripherals.
-
- Posibus peripherals introduced after the PDP-8/L (and also used
- with posibus versions of the PDP-8/I) included:
-
- -- The TC08 DECtape controller (for 8 TU55 or 4 TU56).
- -- The DF32D fixed head disk controller (a posibus DF32).
- -- The FPP-12 floating point processor.
- -- The TR02 simple magnetic tape control.
- -- The RK08 disk subsystem, 4 disk packs, 831,488 words each.
-
- Survival: Many PDP-8/L systems are in operating condition, some performing
- their original jobs.
-
- ------------------------------
-
- Subject: What is a PDP-12?
-
- Date of introduction: 1969 (February or earlier).
- Date of withdrawal: 1973.
- Total production run: 3500?
- Price: $27,900
-
- Technology: DEC M-series flip Chip modules, as in the PDP-8/I.
-
- Reason for introduction: This machine was developed as a follow-up to
- the LINC-8. Originally it was to be called the LINC-8/I, but
- somehow it got its own number. In effect, it was a PDP-8/I with
- added logic to allow it to execute the LINC instruction set.
-
- Reason for withdrawal: The LAB-8/E and the LAB-11 (a PDP-8/E and a
- PDP-11/20 with lab peripherals) eventually proved the equal of
- the PDP-12 in practice, and LINC compatability eventually proved
- to be of insufficient value to keep the machine alive in the
- marketplace.
-
- Compatability: This machine is fully compatable with the PDP-8/I, with
- additional instructions to flip from PDP-8 mode to LINC mode and
- back. IOT 0 could enable the API, causing trouble with later
- PDP-8 code that assumes IOT 0 is "Clear all flags". Also, the
- DECtape instruction DTLA (6766) becomes part of a stack-oriented
- extension to the instruction set, PUSHJ, on late model (or field
- updated) machines with the KF12-B backplane.
-
- The PDP-12 supported trapping of those LINC functions that were
- emulated by software on the LINC-8. This allowed it to run many
- LINC-8 bootable systems (but not all, due mostly incompatabilities
- in LINKtape support), and it allowed such things as emulation of
- LINKtape instructions for reading and writing disk.
-
- The TC12F Linktape controller could, with appropriate software,
- read or write DECtape. This support is unreliable, and is not
- software compatable with the TC01 or TC08 DECtape controller.
-
- Standard configuration: PDP-8/LINC CPU with 4K of memory, plus 110 baud
- current loop interface, plus output relay registers. In
- addition, the standard configuration included either two TU55 or
- one TU56 drive, with a PDP-12 only controller allowing it to
- handle LINCtape. In addition, a 12" scope was always included,
- with a connector that can connect to a second scope.
-
- Expandability: An analog to digital converter and multiplexor was needed
- to fully support knob-oriented LINC software.
-
- Other options included:
-
- -- the KW12 programmable lab clock.
- -- additional TU55 or TU56 drives (up to 8 transports).
- -- the BA12 expander box
- -- the PC05 paper tape reader punch (needs the BA12).
-
- Fabritek made a 24K memory box that could be added to a PDP-8/I or
- PDP-12.
-
- Survival: A few PDP-12 systems are in operating condition.
-
- ------------------------------
-
- Subject: What is a PDP-8/E?
-
- Date of introduction: 1970 (during or before August).
- Date of withdrawal: 1978.
- Also known as:
- PDP-8/OEM
- Industrial-8 (with a red color scheme)
- LAB-8/E (with a green color scheme)
- Price: $6,500
-
- Technology: SSI and MSI TTL logic were used on these boards, and the
- entire CPU fit on 3 boards. Nominally, these were DEC M-series
- flip Chip modules, but in a new large format, quad-high (10.5
- inch), extended-length (9 inch, including card-edge connector,
- excluding handles). The terms used for board height and length
- are based on the original working assumption that all flip-chips
- were plugged horizontally into a vertially mounted card-edge
- connector. On the PDP-8/E, the cards were plugged vertically
- down into a horizontally mounted connector, so many users
- incorrectly refer to these boards as quad-wide double-high.
-
- Interconnection between boards was through a new bus, the OMNIBUS.
- This eliminated the need for a wire-wrapped backplane, since all
- slots in the bus were wired identically. A new line of peripheral
- interfaces was produced, most being single cards that could be
- plugged directly into the inside the main enclosure. These
- included a set of posibus adapters allowing use of older
- peripherals on the new machine.
-
- Interboard connectors were needed for some multiboard options,
- including the CPU and memory subsystems. These used standard
- 36-pin backplane connectors on the opposite side of the board
- from the backplane. Some boards, notably memory boards, had a
- total of 8 connector fingers, 4 for the omnibus and 4 for
- interboard connectors.
-
- The core memory cycle time was 1.2 or 1.4 microseconds, depending
- on whether a read-modify-write cycle was involved (a jumper would
- slow all cycles to 1.4 microseconds). A 4K core plane was
- packaged on a single quad-wide double-high board, with most of
- the drive electronics packed onto two adjacent boards. Soon after
- the machine was introduced, an 8K core plane was released in the
- same format.
-
- Reason for introduction: The cost of the PDP-8/I and PDP-8/L was
- dominated by the cost of the interconnect wiring, and this cost
- was high as a result of the use of small circuit boards. By
- packing a larger number of chips per board, similar function
- could be attained in a smaller volume because less interboard
- communication was required. The PDP-8/E exploited this to achieve
- a new low in cost while attaining a new high in performance.
-
- Reason for withdrawal: This machine was slowly displaced by the PDP-8/A
- as the market for large PDP-8 configurations declined in the face
- of pressure from 16 bit mini and microcomputers.
-
- Compatability: As with the PDP-8/I and PDP-8/L, there are no limits on
- the combination of IAC and rotate instructions. Unlike the early
- machines, basic Group 3 OPR operations for loading and storing
- the MQ register work even if there is no extended arithmetic
- element. Finally, a new instruction was added, BSW; this swaps
- the left and right bytes in AC, and is encoded as a Group 1 OPR
- instruction using the "double the shift count bit".
-
- An odd quirk of this machine is that the RAL RAR combination ands
- the AC with the op-code, and the RTR RTL combination does an
- effective address computation loading the high 5 bits of AC with
- the current page and the lower bits of AC with the address field
- of the instruction itself!
-
- The EAE has a new mode, mode B. Previous EAE designs were
- single-mode. Mode B supports a large set of 24 bit operations
- and a somewhat more rational set of shift operations than the
- standard EAE. All prior EAE designs would hang on the microcoded
- CLA NMI (clear/normalize) instruction applied to a nonzero AC.
- This instruction is redefined to be a mode changing instruction
- on the 8/E.
-
- Standard configuration: A CPU with 4K of memory, plus 110 baud current
- loop teletype interface. Both a rack-mount table-top versions
- were sold (both 9" high by 19" wide by 21" deep). The rack mount
- version was mounted on slides for easy maintenance. The OMNIBUS
- backplane was on the bottom, with boards inserted from the top.
-
- The PDP-8/OEM had a turn-key front panel, no core, 256 words of
- ROM and 256 words of RAM, and was priced at $2800 in lots of 100.
-
- The standard OMNIBUS backplane had 20 slots, with no fixed
- assignments, but the following conventional uses; certain board
- sets were jumpered together (shown with brackets) and therefore
- were required to be adjacent to each other:
-
- -- KC8E programmer's console (lights and switches)
- -- M8300 \_ KK8E CPU registers
- -- M8310 / KK8E CPU control
- --
- --
- -- M833 - Timing board (system clock)
- -- M865 - KL8E console terminal interface.
- --
- --
- -- -- space for more peripherals
- --
- --
- -- M849 - shield to isolate memory from CPU
- -- G104 \
- -- H220 > MM8E 4K memory
- -- G227 /
- --
- -- -- space for more memory
- --
- -- M8320 - KK8E Bus terminator
-
- Most of the early boards with 3 digit numbers were defective
- in one way or another, and the corrected boards added a trailing
- zero. Thus, the M833 was generally replaced with an M8330, and
- the M865 was replaced with the M8650.
-
- Expandability: The following are among the OMNIBUS boards that could be
- added internally:
-
- -- M8650 - KL8E RS232 or current loop serial interface.
- -- M8340 \_ Extended arithmetic element.
- -- M8341 / (must be attached in two slots between CPU and M833.
- -- M8350 - KA8E posibus interface (excluding DMA transfers).
- -- M8360 - KD8E data break interface (one per DMA device).
- -- M837 - KM8E memory extension control (needed for over 4K).
- -- M840 - PC8E high speed paper tape reader-punch interface.
- -- M842 - XY8E X/Y plotter control.
- -- M843 - CR8E card reader interface.
-
- There were many other internal options. There was room in the
- basic box for another 20 slot backplane; taking into account the
- 2 slots occupied by the M935 bridge between the two backplanes,
- this allowed 38 slots, and a second box could be added to
- accomodate another 38 slot backplane, bridged to the first box by
- a pair of BC08H OMNIBUS extension cables.
-
- Given a M837 memory extension control, additional memory could be
- added in increments of 4K by adding G104, H220, G227 triplets.
- The suggested arrangement of boards on the OMNIBUS always
- maintained the M849 shield between memory other options. The
- one exception was that the M8350 KA8E and M8360 KD8E external
- posibus interfaces were typically placed at the end of the
- OMNIBUS right before the terminator.
-
- The following options were introduced later, and there were many
- options offered by third party suppliers.
-
- -- G111 \
- -- H212 > MM8EJ 8K memory
- -- G233 /
- -- M8357 -- RX8E interface to RX01/02 8" diskette drives.
- -- M7104 \
- -- M7105 > RK8E RK05 Disk Interface
- -- M7106 /
- -- M8321 \
- -- M8322 \ TM8E Magtape control for 9 track tape.
- -- M8323 /
- -- M8327 /
-
- Survival: It is still fairly common to find PDP-8/E systems on the
- surplus market, recently removed from service and in working
- condition or very close to it. A modest number are still in
- service doing their orignal jobs, and there is still a limited
- amount of commercial support from both DEC and third-party vendors.
-
- ------------------------------
-
- Subject: What is a PDP-8/F?
-
- Date of introduction: 1972.
- Date of withdrawal: 1978.
-
- Technology: an OMNIBUS machine, as with the PDP-8/E. First use
- of a switching power supply in the PDP-8 family.
-
- Reason for introduction: The PDP-8/E had a large enough box and a large
- enough power supply to accomodate a large configuration. By
- shortening the box and putting in a small switching power supply,
- a lower cost OMNIBUS machine was possible.
-
- Reason for withdrawal: The PDP-8/A 800 displaced this machine, providing
- similar expansion capability at a lower cost.
-
- Compatability: The PDP-8/F used the PDP-8/E CPU and peripherals.
-
- Standard configuration: Identical to the PDP-8/E, except that the KC8E
- front panel was replaced with a KC8M front panel that had LEDs
- instead of incandescent lights; this front panel could also be
- installed on PDP-8/E systems, but the PDP-8/E front panel could
- not be used on a PDP-8/F because of the lack of a +8 supply for
- the lights. The original PDP-8/F box had a defective power
- supply, but a revised (slightly larger) box corrected this
- problem.
-
- With the dintroduction of the M8330, DEC began to require that
- this board be placed adjacent to the KC8x front panel, although
- many OMNIBUS PDP-8 systems continued to be configured (by users)
- with the M8330 elsewhere on the bus. As a result, the suggested
- order of boards on the omnibus began with:
-
- -- KC8E programmer's console (lights and switches)
- -- M8330 - Timing board (system clock)
- -- M8340 \_ optional EAE board 1
- -- M8341 / optional EAE board 2
- -- M8310 \_ KK8E CPU control
- -- M8300 / KK8E CPU registers
- -- M837 - Extended Memory & Time Share control
-
- Expandability: This machine could be expanded using all PDP-8/E OMNIBUS
- peripherals, including the external expansion chassis. The
- relatively small internal power supply and the lack of room for
- a 20 slot bus expander inside the first box were the only
- limitations. There were minor compatability problems with some
- options, for example, the power-fail auto-restart card, as
- originally sold, was incompatable with the PDP-8/F power supply.
-
- Survival: As with the PDP-8/E, these machines are moderately common on
- the surplus market, and frequently in working condition.
-
- ------------------------------
-
- Subject: What is a PDP-8/M?
-
- Date of introduction: 1972.
- Date of withdrawal: 1978.
-
- Technology: This machine was a PDP-8/F (with a PDP-8/E CPU)
-
- Reason for introduction: DEC knew that OEM customers were an important
- market, so they packaged the PDP-8/F for this market, with no
- hardware changes behind the front panel.
-
- Reason for withdrawal: Same as the PDP-8/F
-
- Compatability: The PDP-8/M used the PDP-8/E CPU and peripherals.
-
- Standard configuration: Identical to the PDP-8/F, except that the KC8M
- front panel was replaced with a minimal function panel and the
- color scheme was different. Because of this, one of the following
- options were required:
-
- -- M848 -- KP8E Power fail and auto-restart.
- -- M847 -- MI8E Hardware Bootstrap Loader.
-
- Expandability: All options applying to the PDP-8/F applied. In
- addition, the KC8M front panel (standard with the PDP-8/F) was
- available as an option; the only difference between a PDP-8/F
- and a PDP-8/M with the KC8M front panel was in the artwork on
- the front panel and on the serial number and configuration
- stickers on the back of the box.
-
- Survival: As with the PDP-8/F.
-
- ------------------------------
-
- Subject: What is a PDP-8/A?
-
- Date of introduction: 1974 (Announced in May for December delivery)
- Date of withdrawal: 1984
- Also known as:
- KIT-8/A (CPU plus 1K RAM)
- CLASSIC (CLASSroom Interactive Computer)
- DECDataSystem310 (an 8/A 500 sold as a word-processor)
- Price: $1,835
-
- Technology: This machine used the OMNIBUS with a new single-board CPU.
- The backplane was reoriented so that boards plugged into it from
- the front, with the board held horizontally. The new omnibus
- allowed a board format half again as wide as the original
- (formally, this was called hex height), but the extra 2 groups
- of contact fingers added to each wide board was largely unused.
- (the 6th contact group was not connected on most backplane slots;
- the 5th was unsupported on 8 of the 12 or 20 backplane slots, and
- was used primarily for additional power and ground distribution).
-
- Reason for introduction: Using TTL MSI and LSI components, DEC was able
- to reduce the PDP-8 CPU to a single oversize board (formally, hex
- height, double width). Similarly, they were able to make an 4K
- core memory board, and later, an 8K board in this format, and they
- were able to introduce a static RAM card using semiconductor
- memory. The minimum system was thus reduced to 3 boards. The
- relatively expensive lights and toggle switches on the front panel
- of the PDP-8/E were replaced with an octal membrane keypad and
- 4-digit 7-segment LED display.
-
- The market for the PDP-8 was dominated by small systems, with
- fewer and fewer customers needing large-scale expandability.
- Thus, the 20 slot backplane of the early OMNIBUS machines was too
- big; with the new single board CPU and memory, a 12 slot backplane
- was enough, allowing further cost reductions.
-
- Reason for withdrawal: The market for the PDP-8 family was shrinking in
- the face of pressure from larger minicomputers and the new
- monolithic microcomputers. After 1975, many PDP-8 sales were to
- captive customers who had sufficient software investments that
- they could not afford to move. Only the word-processing and
- small business markets remained strong for first-time PDP-8
- sales, and in these, the specialized DEC VT-78 and DECmate
- machines were more cost effective than the open architecture
- OMNIBUS machines.
-
- Compatability: The new PDP-8/A CPU was largely compatable with the
- PDP-8/E CPU, except that the combination of RTR and RTL (Group 1
- OPR instructions) loaded the next address. The power-fail
- auto-restart option included the standard skip on power low
- instruction, but also a new skip on battery empty instruction to
- test the battery used for back-up power on the new solid state
- memory.
-
- The standard parallel port on the M8316 was not software
- compatable with the earlier line-printer interfaces used with
- device code 66.
-
- Standard configurations: The PDP-8/A was sold with a new short OMNIBUS
- backplane, mounted on its side above a power supply and a
- battery to back up the solid state memory. The minimum
- configuration included a limited function control panel and the
- following components on the bus:
-
- -- M8315 -- KK8A CPU board
- -- M???? -- MS8A 1K to 4K solid state memory.
- -- M???? -- MR8A ROM companion for the MS8A.
- -- M8316 -- DKC8AA serial/parallel interface and clock.
-
- The M8316 board contained a remarkable but useful hodgepodge of
- commonly used peripherals, including the console terminal
- interface, a parallel port, the power/fail auto-restart logic,
- and a 100 Hz real time clock.
-
- The smallest PDP-8/A configuraton marketed was the KIT/8A, either
- just the KK8A and MS8A 1K boards for $572, or $1350 for a system
- that appears to have included the M8316 and a 4 slot backplane.
-
- The 8/A 100, was a computer system with a 10 slot backplane
- and a poor power supply. The 8/A 400 was a better system with
- a 12 slot backplane, and the 8/A 420 had a 20 slot backplane.
- The 8/A 600 and 620 were the 8/A 400 and 420 with the KK8E
- PDP-8/E CPU set allowing added speed and the use of the 8/E EAE.
-
- Expandability: All PDP-8/E peripherals and options could be used with
- the PDP-8/A. For those configurations requiring more than 20
- backplane slots, A pair of PDP-8/A backplanes could be connected
- using BC08H cables, and there was a special cable, the BC80C,
- for connecting a hex wide 8A backplane to a PDP-8/E, -8/F or
- -8/M backplane.
-
- By February 1975, the PDP-8/A was being sold in a workstation
- configuration, with the CPU and dual 8" diskette drives in a desk
- with a video terminal (VT52) and optional letter quality printer
- on top. For the educational market, this configuration was
- marketed as the CLASSIC. As an office system, such configurations
- were marketed as DECDataSystems.
-
- The following additional PDP-8/A (hex) boards were offered:
-
- -- G649 \_ MM8AA 8K Core stack (too slow for 8/E CPU!).
- -- H219A / MM8AA 8K Core memory control.
- -- G650 \_ MM8AB 16K Core stack (ok for 8/E CPU!).
- -- H219B / MM8AB 16K Core memory control.
- -- M8349 -- MR8F 1K ROM (quad, overlayable with core).
- -- M8317 -- KM8A memory extender (with variations).
- -- M8319 -- KL8A 4 channel RS232 or current loop serial I/O.
- -- M8433 -- RL8A controller for 1 to 4 RL01/RL02 disk drives.
- -- M8410 \_ FPP8A floating point processor control
- -- M8411 / FPP8A floating point processor data path
-
- The PDP-8/A model 800 was the same as the model 600, but with the
- FPP8A floating point processor included as part of the package.
-
- -- M8416 -- KT8AA Memory management unit for up to 128K.
- -- -- KC8AA Programmer's Console (requires M8316)
- -- M8417 -- MSC8DJ 128K DRAM MOS Memory.
-
- Note that memory extension to 128K was a new PDP-8/A feature that
- was necessarily incompatable with the older PDP-8 memory expansion
- options, although the conventional PDP-8 memory expansion
- instructions still operate correctly on the first 32K. Access to
- additional fields involved borrowing IOT instructions that were
- previously dedicated to other devices.
-
- The MM8A core memory options require the use of a box with a G8018
- power supply that provides +20V, while the semicondustor memory
- options require a G8016 power supply with built-in battery backup.
- Also, the use of the MSC8 DRAM memory cards require a CPU that
- supports the memory stall signal; early PDP-8/E CPUs did not.
-
- Survival: As with the PDP-8/E, these machines are moderately common on the
- surplus market and a modest number are still in use.
-
- ------------------------------
-
- Subject: What is a VT78?
-
- Date of introduction: 1978
- Date of withdrawal: 1980 (Displaced by the DECmate)
- Also known as:
- DECstation
- DECstation 78
- Price: $7,995 ($5,436 in lots of 100)
-
- Technology: Based on the Intersil/Harris 6100 microprocessor, packaged
- in a VT52 case. The 6100 processor was able to run at 4 MHz, but
- in the VT78, it was only clocked at 2.2 MHz because of the speed
- of the DRAM used and the deliberate use of graded out chips.
-
- Reason for introduction: Using TTL MSI and LSI components, DEC could
- pack a system into the vacant space in a standard terminal case,
- allowing PDP-8 systems to compete with personal computers in the
- small business and office automation market. This was a natural
- follow-on to the desk-mounted workstation configurations in which
- the PDP-8/A was already being sold.
-
- Compatability: The Group I OPR combinations RAL RAR and RTL RTR are
- no-ops. Unlike all earlier PDP-8 models, autoindex locations
- 10 to 17 (octal) only work in page zero mode; these operate like
- all other memory locations when addressed in current page mode
- from code running on page zero. Other than this, it is fully
- PDP-8/E compatable, even at the level of I/O instructions for
- the standard periperals; this was the last PDP-8 to offer this
- level of compatability.
-
- It was not possible to continue from a halt without restarting
- the machine. In addition, none of the peripherals available on
- this machine needed DMA (data break) transfers.
-
- Standard configuration: The VT78 was sold with 16k words of DRAM with
- the keyboard and display of the VT52 terminal. An RX01 dual 8"
- diskette drive was included, packaged in a teacart pedestal under
- the terminal. The console (device 03/04) and the serial ports
- (devices 30/31 and 32/33) are compatible with the M8650 KL8E,
- with the latter extended to allow software controlled baud rate
- selection. There are two parallel ports; device 66 (compatible
- with the M8365 printer controller) and device 47, compatible with
- the nonstandard port on the M8316 DKC8AA. There is also a 100Hz
- clock compatible with the clock on the M8316 DKC8AA.
-
- The standard ROM boots the system from the RX01 after setting the
- baud rates to match that selected by the switches on the bottom
- of the VT52 case.
-
- Expandability: This was a closed system, with few options. The base
- configuration was able to support two RX01 drives (later RX02),
- for a total of 4 transports. Various boot ROM's were available,
- including a paper-tape RIM loader ROM for loading diagnostics
- from tape. Another ROM boots the system from a PDP-11 server in
- the client/server configuration used by WPS-11.
-
- Survival: There are probably many VT78 systems still in use.
-
-
- ------------------------------
-
- Subject: What is a DECmate I?
-
- Date of introduction: 1980
- Date of withdrawal: 1984 (Phased out in favor of the DECmate II)
- Also known as: DECmate (prior to the DECmate II, no suffix was used)
- VT278
-
- Technology: Based on the Harris 6120 microprocessor, packaged in a
- VT-100 box with keyboard and display.
-
- Reason for introduction: This machine was aimed primarily at the market
- originally opened by the VT78, using a new gate-array implementation
- of the PDP-8 built under contract with DEC by Harris. The Harris
- 6120 was designed to run at 10 Mhz, and the new packaging was
- optimized for minimum cost and mass production efficiency.
-
- Compatability: A new feature was introduced in the 6120 microprocessor:
- The Group I OPR combination RAL RAR was defined as R3L, or rotate
- accumulator 3 places left, so that byte swap (BSW) is equivalent
- to R3L;R3L. RTR RTL remained a no-op, as in the 6100.
-
- Also, the EAE operations not implemented in the basic CPU cause
- the CPU to hang awaiting completion of the operation by a
- coprocessor. Unfortunately, no EAE coprocessor was ever offered.
-
- The printer port offered software baud-rate selection compatable
- with the VT78 baud-rate selection scheme. The dual-port data
- communications option was flexible but completely incompatable
- with all previous PDP-8 serial ports.
-
- The console and printer ports are not fully compatable with the
- earlier PDP-8 serial ports. Specifically, on earlier serial
- interfaces, it was possible to test flags without resetting them,
- but on the DECmate machines, testing the keyboard input flag
- always resets the flag as a side effect. In addition, on the
- console port, every successful test of the flag must be followed
- by reading a character or the flag will never be set again.
-
- It was not possible to continue from a halt without restarting
- the machine.
-
- The large amount of device emulation performed by the CPU in
- supporting screen updates severely limits the ability of the
- system to run in real time.
-
- Standard configuration: The DECmate I was sold with 32k words of memory,
- with a small control memory added to handle control/status,
- console device emulation and boot options. The console terminal
- keyboard and display functions are largely supported by code
- running in control memory (a less expensive alternative to
- dedicating hardware for this, as was done in the VT78).
-
- The DECmate I came with an integral printer port, compatable with
- the VT78 (device 32/33), and it had an RX02 dual 8 inch diskette
- drive, mounted in the short pedistal under the terminal/CPU box.
- A 100Hz clock was included, as in the VT78 and PDP-8/A.
-
- Expandability: This was a closed system, with limited options.
- Specifically, a second RX02 could be connected (or an RX01,
- because that had a compatable connector), the DP278A and DP278B
- communications boards (really the same board, but the DP278B had
- 2 extra chips), and the RL-278 disk controller, able to accomodate
- from 1 to 4 RL02 rack mount disk drives.
-
- When the DP278A option is added, additional routines in control
- memory come alive to handle terminal emulaton and allow diskless
- operation. The terminal emulator is an extended VT100 subset
- that is essentially compatable in 80 column mode. The DP278A
- option could support both asynchronous and synchronous protocols,
- and the DP278B could handle SDLC and other nasty bit-stuffing
- protocols.
-
- Various pedestal and desk configurations were sold for housing
- the RX01 and RX02 drives, most being teacart style designs, but
- there was also a pedestal version that was essentially a
- repackaging of the RX02 with either 2 or 4 new 8 inch disk
- transports (physically incompatable with earlier DEC transports).
-
- Survival: Many DECmates are still in use, and they are fairly common on
- the surplus market. They are found in small numbers just about
- anywhere large numbers of early PC vintage machines are found.
-
- ------------------------------
-
- Subject: What is a DECmate II?
-
- Date of introduction: 1982
- Date of withdrawal: 1986
- Also known as:
- PC27X series.
- Price: $1,435
-
- Technology: Based on the 6120 microprocessor, this shared the same
- packaging as DEC's other competitors in the PC market, the
- Rainbow (8088 based) and the PRO-325 (PDP-11 based).
-
- Reason for introduction: This machine was introduced in order to allow
- more flexibility than the DECmate I and to allow more sharing of
- parts with the VT220 and DEC's other personal computers.
-
- Compatability: Same as the DECmate I, except it could continue from a
- halt. There was better hardware for device emulation support,
- allowing for somewhat better real-time performance. The data
- communications port was an incompatable improvement on the
- incompatable DECmate I communications port. No built-in terminal
- emulation was provided, and the data communications port supported
- only one line, but aside from this, the data communications port
- is essentially as powerful as the DP-278B on the DECmate I.
-
- Standard Configuration: The DECmate II was sold with 32K of program
- memory, plus a second full bank for dedicated control panel
- function emulation. Code running in the second bank is sometimes
- referred to as slushware; it looks like hardware to the PDP-8
- user, but it is actually device emulation software that is loaded
- from the boot diskette.
-
- An integral RX50 dual 5 1/4 inch diskette drive with an 8051
- controller chip was included, along with a printer port, a 100Hz
- real-time clock, single data communications port, and interfaces
- to the monitor and keyboard. The diskette drive can read
- single-sided 48 track-per-inch diskettes, so it might be possible
- to read (but not write) IBM PC diskettes on it.
-
- Expandability: This was the most open of the DECmate systems, with a
- number of disk options: An additional pair of RX50 drives could
- be added, and with the RX78 board, it could support a pair of
- dual 8 inch drives, either RX01 or RX02.
-
- As an alternative to the RX78, there was a controller for an
- MFM hard drive. The interface to the RX78 board wasn't fully
- compatable with earlier interfaces to RX01 and RX02, and there
- was no way to have both an RX78 and an MFM drive. The MFM drive
- could be up to 64 MB, with 16 sectors per track, 512 bytes each
- and at most 8 heads and 1024 (or possibly 4096) cylinders. A
- power supply upgrade was needed to support the MFM drive. DEC
- sold this machine with 5, 10 and 20 meg hard drives, Seagate
- ST-506, 412, and 225 respectively.
-
- A graphics board supporting a color monitor could be added in
- addition to the monochrome console display; two variants of
- this board were produced during the production run, all slightly
- incompatable.
-
- A coprocessor board could be added, with communication to and
- from the coprocessor through device 14. DEC sold three boards,
- an APU board (Z80 and 64K), and two XPU boards (Z80, 8086 and
- either 256K or 512K). If these added processors are used, the
- 6120 processor is usually used as an I/O server for whatever
- ran on the coprocessor. The XPU boards used a Z80 for I/O
- support, so 8086 I/O was very indirect, particularly if it
- involved I/O to a PDP-8 device that was emulated from control
- memory. Despite this, the DECmate version of MS/DOS is generally
- faster than MS/DOS on more recent 80286 and 80386 based IBM PCs
- because of effective use of the coprocessors (but they couldn't
- run MS/DOS code that bypasses MS/DOS for I/O).
-
- Survival: As with the DECmate I.
-
- ------------------------------
-
- Subject: What is a DECmate III?
-
- Date of introduction: 1984
- Date of withdrawal: 1990
- Also known as:
- PC23P-Ax/LH -- where x gave the monitor color A (B/W), J(Grn), S(Amb).
- Price: $2,695 - $2885
-
- Technology: Same as the DECmate II.
-
- Reason for introduction: Again, DEC discovered that the market for large
- systems was dominated by other products, and that the PDP-8 based
- products were rarely expanded to their full potential. Thus,
- there was no point in paying the price for expandability.
-
- Compatability: Same as the DECmate II, except that the printer port is
- fixed at 4800 baud.
-
- Standard Configuration: The DECmate III was sold with 32K of program
- memory, plus a second full bank for dedicated control panel
- functions, an integral RX50 dual 5 1/4 inch diskette drive with
- an 8051 controller chip, a printer port, a 100Hz real-time-clock,
- a data communications port, and interfaces for the VR-201 monitor
- and keyboard.
-
- Expandability: A revised version of the Z80 based coprocessor for the
- DECmate II was available for $430 (PC23X-AB/LH), and a graphics
- board largely compatable with the later DECmate II graphics board
- could be added for $630 (PC23X-CA/LH), allowing the standard
- monochrome monitor to be replaced with a VR-241 color monitor.
- Dual monitor configurations were not supported. An obscure
- variant of the DEC scholar modem was also supported for $630
- (PC23X-DA/LH).
-
- Survival: As with the DECmate I.
-
- ------------------------------
-
- Subject: What is a DECmate III+?
-
- Date of introduction: 1985
- Date of withdrawal: 1990
- Also known as:
- PC24P-Ax/LH -- where x gave the monitor color A (B/W), J(Grn), S(Amb).
- Price: $5,145
-
- Technology: Same as the DECmate II.
-
- Reason for introduction: This machine apparently represents the last
- gasp of the PDP-8, hunting for the remains of the ever-shrinking
- market niche that the earlier DECmates had carved out. The
- market niche was not there, and the production runs for this
- machine were short enough that UV erasable EPROM technology was
- used where earlier DECmates had used mask programmed chips.
-
- Compatability: Same as the DECmate II, but the machine was unable to
- read 48 track per inch IBM formatted diskettes. Again the
- printer port was fixed at 4800 baud.
-
- Standard Configuration: The DECmate III+ was sold with 32K of program
- memory, plus a second bank for dedicated control panel functions,
- an integral RX33 single 5 1/4 inch diskette drive with an 8751
- controller chip, a printer port, a data communications port and
- interfaces to the monitor and keyboard. A hard disk controller
- compatable with the optional one on the DECmate II was included,
- supporting an integral ST-225 20 MB disk; it is likely that it
- can only handle up to 1024 cylinders, but it is otherwise
- compatable with the DECmate II.
-
- Expandability: The same coprocessor option sold with the DECmate III was
- available, but because of the difficulty of adding a second floppy
- drive, this was rarely used (the Z80 was most likely to be used
- to run CP/M, but that system requires two drives to handle the
- installation procedure; an appropriately configured bootable
- image created on a DECmate II or III could run on a DECmate III+).
-
- The same graphics board as used on the DECmate III was also
- available. The circuit traces and connectors for the Scholar
- modem are present, but this option was never sold on the
- DECmate III+.
-
- Survival: As with the other DECmates.
-
- ------------------------------
-
- End of PDP-8 Summary of Models and Options (posted every other month)
- *********************************************************************
-