Internet Info 1994 March/Internet Info CD-ROM (Walnut Creek) (March 1994).iso/answers/alt/dec-faq/pdp8-models

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From: [e-mail] (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: Tue, 8 Apr 94 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: bloom-beacon.mit.edu alt.sys.pdp8:745 alt.answers:2365 news.answers:17830

Archive-name: dec-faq/pdp8-models
Last-modified: Apr 7, 1994

This version of the alt.sys.pdp8 FAQ has been modified to conform to
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Contents:

    What is this FAQ?
    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 this FAQ?

Frequently Asked Questions about DEC PDP-8 models and options.

    By Douglas Jones, [e-mail]
    (with help from many folks)

Sites known to carry FTPable copies of this file:

    ftp://rtfm.mit.edu/pub/usenet/alt.sys.pdp8
    ftp://sunsite.unc.edu:/pub/academic/computer-science/history/pdp-8/doc

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 systems.

------------------------------

Subject: What is a PDP-5?

Date of introduction:  Aug 11, 1963, unveiled at WESCON.
Date of withdrawal:    early 1967.
Price: $27,000

Technology:  Built with DEC System Modules, the original line of
    transistorized logic modules sold by DEC.  Supply voltages of
    +10 and -15 volts; the logic levels -3 (logic 1) and 0 (logic 0).
     Logic packaged on boards that were about 4.75 inches wide 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.

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 did not support 3 cycle data-break (DMA transfers using
    memory to hold buffer address and word-count information), so
    many later PDP-8 peripherals could not 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 DECtape transports
    were originally developed for the PDP-5.

    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.

------------------------------

Subject: What is a PDP-8?

Date of introduction:  1965 (Unveiled March 22, in New York)
Date of withdrawal:    1968.
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 Foxboro Corporation.
Price: $18500

Technology:  Mostly 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 discrete components on the PC
    boards, and DEC began to refer to their R-series modules as
    flip-chip modules and 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.

    S-series logic modules were also used; these are essentially
    the same as their R-series cousins, but with different pull-up
    resistors for higher speed at lower fanout.  Many R and S
    series modules have trimmers that must be tuned to the context,
    making replacement of such modules more complex than a simple
    board swap.

    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 high.  The card edge connector
    had 18 contacts on 1/8 inch centers.  Some double width cards
    were used; these had two card edge connectors and were 5 1/8
    inches wide.  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.  4
    (originally 5) more bundles were required to support data-break
    (DMA) transfers.  Bus termination was generally kluged in with
    100 ohm resistors clipped or wrapped into the backplane,
    although a bus terminator card was occasionally used.  Some time
    after the first year of production, flat ribbon cable made of
    multiple coaxial cables was used, and later still, flat mylar
    stripline cable was used (but never recommended because it
    lacked necessary shielding).

    Core memory was used, 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 for support.  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:  The core of the PDP-8 instruction set is present, but
    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.

    If the extended arithmetic element is present, the SWP (exchange
    AC and MQ) instruction does not work.  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, basic machine occupied a volume 33 inches high by 19
    inches wide by 22 inches deep.  The two halves of the backplane
    were 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.

Expandability:  In-cabinet options include the type 182 extended
    arithmetic element (EAE), the type 183 memory extension control
    subsystem, and the type 189 low performance analog to digital
    converter (ADC).  Prewired backplane slots were reserved for
    all of these.

    Expansion beyond 4K of memory requires rack space for the
    rack-mounted type 184 memory module; each such module adds one
    4K field of memory, up to a maximum of 32K.  The rack-mount CPU
    occupied a large part of one rack, allowing room for a single
    type 184 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 750C high speed paper tape reader and control.
    -- Type 75E high speed paper tape punch and control.
    -- Type 138E analog to digital converter and multiplexor.
    -- Type 34D oscilloscope display (dual digital to analog).
    -- Type 350B incremental (CalComp) plotter control.
    -- Type 451 card reader and control.
    -- Type 450 card punch control for IBM Type 523 punch.
    -- Type 64 (later 645) Mohawk line printer and control.
    -- Type RM08 serial magnetic drum system (up to 256K words).
    -- Type 552 DECtape control (for type 555 DECtape drives).
    -- Type 57A magnetic tape control (IBM type 729 drive).
    -- Type 580 magnetic tape system.

    By 1967, the following peripherals had been added to the line:

    -- Type TC01 DECtape control for up to 8 TU55 transports.
    -- Type AF01 analog to digital converter and multiplexor.
    -- Type AA01A 3 channel digital to analog (scope display).
    -- 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 (up 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.

------------------------------

Subject: What is a LINC-8?

Date of introduction:  1966 (during or before March)
Date of withdrawal:    1969 (displaced by PDP-12)
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:  Identical to the PDP-8.

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.
    Each pair of drives cosmetically resembled the type BE03 dual
    DECtape transport, but single drives were not available.

    Up to 2 additional ranks of 8 ADC channels could be added.

    A second oscilliscope could be added.

------------------------------

Subject: What is a PDP-8/S?

Date of introduction:  1966 (Unveiled, Aug 23, WESCON, Los Angeles).
Date of withdrawal:    1970.
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 was mounted on quad-height
    single-width boards that plugged into the standard flip-chip
    sockets.

Reason for introduction:  This machine was developed as a successful
    exercise in minimizing the cost of the machine.  It was the
    least expensive general purpose computer 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.  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 table-top
    versions were sold (both 9" high by 19" wide by 20"? deep).  The
    rack mount could be slid out of the rack on slides for 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.

------------------------------

Subject: What is a PDP-8/I?

Date of introduction:  1968 (announced before December '67)
Date of withdrawal:    1971.

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 supply, packaged on the same format board
    as was 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
    whether the fetch was from an even or odd field.

Standard configuration:  CPU with 4K of memory, plus 110 baud current
    loop teletype interface.  Pedestal, rack-mount and table-top
    versions were made.  The pedestal mounted version was futuristic
    looking, compatable with such office fixtures as decwriters.
    In one rack-mount version, the machine was built on a backplane
    that was bolted to the back of the rack, while the front panel
    hung from the front (unlike all other rack-mounted PDP-8 models,
    this version could not be swung out for maintenance on chassis
    slides).  Finally, a boxed version was sold that could be used
    on table-top or mounted on chassis slides.

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.

    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 DEC made an effort to convert earlier machines to the posibus
    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 systems 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.  To add to this confusion, some negibus
    PDP-8/I systems were rewired to use 18 conductor posibus cables
    while still using 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.

------------------------------

Subject: What is a PDP-8/L?

Date of introduction:  1968 (announced before August '68)
Date of withdrawal:    1971.
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 the memory cycle cycle time was
    downgraded to 1.6 microseconds to avoid the speed problems of
    the -8/I.

    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 mylar ribbon cable in most cases.  Electrically, coaxial
    cable could be used, but the slots in the CPU box were too small
    to allow convenient use of this option.

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 the
    PDP-8/I Calcomp plotter interface.

    DEC eventually offered the BM12L, an 8K expansion box, allowing
    12K total memory on a PDP-8/L.  Curiously, 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 TC08P DECtape controller (for 8 TU55 or 4 TU56).
    -- The DF32D-P 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.

------------------------------

Subject: What is a PDP-12?

Date of introduction:  1969 (February or earlier).
Date of withdrawal:    1973.
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 most of the LINC instruction
    set, with trapping and software emulation used more selective
    than on the LINC-8.

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.

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 additoon, 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 PRTC12F option to allow DECtape as well as LINCtape.
    -- the PC05 paper tape reader punch.

------------------------------

Subject: What is a PDP-8/E?

Date of introduction:  1970 (during or before August).
Date of withdrawal:    1978.
Also known as:
    Industrial-8 (with a red color scheme)
    LAB-8/E (with a green color scheme)
Price: $7,390

Technology:  Nominally made from DEC M-series flip Chip modules, but in
    a new format, quad-wide (10.5 inch wide), double-height (9 inch
    high, including card-edge connector, excluding handles).  SSI
    and MSI TTL logic were used on these boards, and the entire CPU
    fit on 3 boards.

    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
    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 OPR instruction!

    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 standard OMNIBUS backplane had 20 slots, with no fixed
    assignments, but the following conventional uses:

    -- 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 adjacent to CPU.
    -- 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 /

    At one point, DEC packaged a PDP-8/E in a desk with no front panel
    controls other than power and bootstrap switch, along with an RX01
    accessable from the front and a VT50 on top.  This was sold as
    the Class-ic system, with an intended market in the classroom
    (hence the name); it was the forerunner, in terms of packaging,
    of many later DEC office products.

------------------------------

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.

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.

------------------------------

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.

------------------------------

Subject: What is a PDP-8/A?

Date of introduction:  1975
Date of withdrawal:    1984

Technology:  This machine used the OMNIBUS with a new single-board CPU,
    made possible by the use of TTL MSI and LSI components on an
    extra-wide board (formally, hex wide, double high) with 6 connector
    fingers instead of the usual 4.

Reason for introduction:  Using TTL MSI and LSI components, DEC was able
    to reduce the PDP-8 CPU to a single hex wide double high card.
    Similarly, they were able to make an 4K core memory card, and
    later, an 8K board in this format, and they were able to introduce
    a static RAM card using semiconductor memory.  The net effect was
    to reduce the minimum system to 3 boards.

    In addition, 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.

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.

Standard configuration:  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.
    -- 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 original configuration sold had a 10 slot backplane and a
    poor power supply.  The later base model had a 12 slot backplane,
    the 8/A 400.

Expandability:  All PDP-8/E peripherals and options could be used with
    the PDP-8/A.  The KK8A cpu was not as fast as the KK8E used in
    the PDP-8/E, but the KK8E CPU could be substituted for the KK8A
    CPU, and many PDP-8/A systems were sold with this substitution.

    A box with a 20 slot backplane, the 8/A 800, was available for
    large configurations.  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 late 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 (VT57?) on top.  This followed the pattern
    set by the Class-ic packaging of the PDP-8/E, but it was aimed
    at the word-processing market.

    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.
    -- M???? -- MR8F 1K ROM (overlayable with RAM).
    -- M8317 -- KM8A memory extender (with variations).
    -- M8319 -- KL8A 4 channel RS232 or current loop serial I/O.
    -- M???? -- RL8A controller for 1 to 4 RL01/RL02 disk drives.

    -- 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 options require the use of a box with a -20V power supply.
    Also, the use of the MSC8 DRAM memory cards requires a CPU that
    supports the memory stall signal, early PDP-8/E CPUs did not.

------------------------------

Subject: What is a VT78?

Date of introduction:  1978
Date of withdrawal:    1980 (Displaced by the DECmate)
Also known as:  DECstation 78

Technology:  Intersil 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 their CPU into 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 location 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 standard, packaged in the pedestal under the
    terminal.  The console (device 03/04), the printer (output only)
    port (device 66), and the serial ports (devices 30/31 and 32/33)
    are compatable with the M8650 KL8E, with the latter extended to
    allow software controlled baud rate selection.  The parallel port
    (device 47) and 100Hz clock are compatable with the comparable
    PDP-8/A options 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.

------------------------------

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 Intersil/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 the IM6120 as a substitute
    for the older 6100 chip and optimizing 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 data communications
    option was 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 additional control memory added to handle
    control/status and boot options.  The console terminal keyboard
    and display functions are largely supported by so-called
    slushware routines in oontrol 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 cabinet 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 control memory is
    included containing a ROM-based terminal emulator allowing
    diskless operation.  The 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 tearlier DEC transports).

------------------------------

Subject: What is a DECmate II?

Date of introduction:  1982
Date of withdrawal:    1986
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 (80x86 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, and the data
    communications port was an incompatable improvement on the
    incompatable DECmate I communications port.  The improved data
    communications port make it essentially as powerful as the
    DP-278B on the DECmate I, with a more efficient but bizarre
    software interface.

Standard Configuration:  The DECmate II was sold with 32K of program
    memory, plus a second full bank for dedicated control panel
    function emulation, an integral RX50 dual 5 1/4 inch diskette
    drive with an 8051 controller chip, 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.

    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).

------------------------------

Subject: What is a DECmate III?

Date of introduction:  1984
Date of withdrawal:    1990
Price: $2,695

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 of 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, and a graphics board compatable with
    the later DECmate II graphics board could be added allowing the
    standard monochrome monitor to be replaced with a VR-241 color
    monitor.  Two monitor configurations were not supported.  An
    obscure variant of the DEC scholar modem was also supported as
    an option.

------------------------------

Subject: What is a DECmate III+?

Date of introduction:  1985
Date of withdrawal:    1990

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 lack of 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+.

------------------------------

End of PDP-8 Summary of Models and Options (posted every other month)
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