Digital Equipment Corporation PDT-11/150 system

    The Digital Equipment Corporation PDT-11/150 (formal designation, PDT-11/150-CH) is an interesting little machine that consists of an LSI-11 CPU chipset, 30 kw of MOS memory and a pair of single density (128 kw, 256 kb) 8" floppy drives. It's configured from four main PC boards: the pdp11 CPU module, the floppy controller, the I/O controller, and the main memory module. These boards are located in the upper "head" area just above the two floppies.

    "PDT", for the record, stands for "Programmable Data Terminal" and was applied to several "family" members, most of which were housed in VT-100 style enclosures; only the -150 sported this particular packaging.

    The CPU module not only contains the 4 IC chipset of the LSI-11, but also has a fully configured 8085A microprocessor which functions as the I/O device controller. The floppy controller module also uses an 8085 chip to operate the two drives.

    The instruction set is that of the basic pdp11/03. There are ports on the back of the machine for the console, a printer, a modem, and (as an option) three slave terminals. The I/O ports are all RS-232 devices.

    DEC offered the PDT-11 in several different models, including ones with reduced memory (16 kw), one floppy drive only, and models that excluded the three slave terminals. An Extended Instruction Set (EIS) model was also available.

    Currently I have a pair of these machines in the collection, one functional and one broken (it has a bad crystal oscillator). The nonfunctional one sports the EIS option which is implemented as a second ROM chip on a dual carrier in the quad chipset of the LSI-11. Both have maximal memory and the optional I/O interfaces.

    The functional PDT-11/150 here runs the RT-11 operating system common to virtually all pdp-11s. Since the machine lacks memory management, it is unable to run the operating systems that use the extended memory made available with this option. The operational machine has a date stamp of "Sep 24 1980" on the CPU board.

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