Digital Equipment Corporation pdp-11/34a processor

    DEC's pdp11/34a is a decent example of the mid-life of the -11 line before the microprocessor-based machines came into prominence (see the pdp-11/03 if you're curious about the microprocessor - based -11s). The /34a is a slightly newer design of the original /34; the two are indistinguishable from one another without looking at the CPU boards.

    The machine is a microcoded implementation of the -11 architecture and utilises TTL logic and a few LSI ROMs which contain the microcode. The CPU itself is contained on 2 hex-height boards which also implement memory management (making possible an 18-bit physical address space). Both Floating Point (FIS) and cache memory options were available, this example having the FIS option installed.

    The basic -11/34 came from the manufacturer bereft of a programmers' console, instead relying on a console emulator running from the boot ROMs in the I/O address space. This emulator allowed the console teletypewriter to act as a "front panel" with simple commands a la ODT. ODT it's not though; that would come later with the microprocessor implementations.

    DEC did make available, as an option, a front panel for the -11/34. This operated as a separate "device" and was implemented on a quad-height board that plugged into the CPU backpanel. This board, in turn, connected to the panel proper via a small cable.

    The basic -11/34a CPU is comprised of two boards: a control module and a data paths module. Both of these are hex-height boards and reside in slots 1 and 2 of the CPU backplane. The FIS board lives in slot three. The FIS board communicates with the data paths module and is operated by commands from the control module by means of jumpers conected on the back of the boards (i.e. opposite the "finger side" which plugs into the backplane).

    This example, as currently configured, contains 48 kw (96 kb) of parity core memory, a DL-11W TTY controller with line clock, a TC-131 9 track tape drive controller (salvaged from a VAX-11/785), the console, and the RX-21 floppy controller. It runs RT-11 and is a big- time power hog.

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