Digital Equipment Corporation pdp-11/23 system

    Digital Equipment Corporation's pdp-11/23 is a Q-bus based LSI (Large Scale Integration) implementation of the standard pdp-11 architecture.

    This specimen started life off as a voice-response controller for one of my employers. The internal configuration consists of 3 double-height boards and a single quad-height module.

    The three double-height boards are:

• M8186 LSI-11/23 CPU
• M8047 Multifunction Module (described below)
• M8029 RXV-21 Floppy Controller

    The quad-height board:

• Clearpoint 1 Mb memory (using Inmos IMS2600P-15 RAM chips)

    Unfortunately, this machine lacks the memory management unit (a single chip, in this case) required to address anything above the standard limit of 28 kw.

    The M8047 Multifunction Module contains ROM-based boot utilities, functions as the Line Clock, and controls the terminal interface, in this case a C. ITOH CIT-220+. The CPU itself contains ODT in its microcode.

    The RXV-21 attaches to an RX-02 unit which serves as the mass storage for this system.

    The machine lives in a pdp-11/03 housing (19" wide, 3 1/2" high, 15" deep) and represents the fastest -11 in the collection, and certainly the one that draws the least power. I imagine the original CPU board was indeed an 11/03 that was upgraded to a /23 later in life by a board swap.

    For those who enjoy the control that only a good front panel can offer, disappointment awaits; there are but 3 switches (Power, Run/Halt, and LTC Enable/Disable) and 2 LEDs (Power and Run).

    The terminal sitting atop the 11/23 is not a VT-220, but rather a "clone" of this venerable device known as a CIT-220+ manufactured by the C. Itoh Electronics Company.

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