Packard Bell Computer
pb 250 Computer

[JPEG image of PB-250]

    In 1961, Packard Bell Computer of Los Angeles introduced this machine. It is, by far, the oldest system in the collection. This example is serial number 119, and has a manufacture date of April 16, 1961 stamped on the power supply. There are slightly more than 60,000 hours on the power meter.

    The machine is constructed from discrete components (transistors, diodes, and resistors) and uses acoustic delay- line memory. It functions in a serial manner, processing one bit at a time. The word width (from a programmer's viewpoint) is 22 bits. From a machine perspective the width is 24 bits, the extra two going for parity and "guard bit" uses. The basic cycle completes in 12 microseconds, with several instructions requiring only that amount of time.

    I was surprised as to the sophistication of the instruction set when I first began to look through the manuals that came with the machine. The 250 is able to do integer multiplication, division, and even square root operations with its basic instruction repertoire. This is the first machine I'd encountered (other than very new ones with maths processors) that had a SQR instruction built into its basic OP- code set. There are also hooks built into it for floating- point operations (e.g. normalisation).

    The memory system on this machine is an amazing thing. The formal term for the storage scheme is "Magnetostrictive Delay Line". It uses acoustic (sound) pulses propagated through a nickel- steel wire and recirculates them electronically. Pulses get put into the wire by a transmitter, make their way through the wire, and emerge at the far end to be picked up by a receiver. The receiver generates an electrical pulse for each "bit" of acoustic energy received that is fed simultaneously to the computational electronics and back to the memory transmitter. The memory is addressed by "Line" and "Sector" notation, the "line" portion referring to which memory module the data are in, the "sector" noting the position of the data in said line. Long lines hold 256 twenty- four bit words, short ones hold 16, and registers hold one.

    All computation is done in a serial fashion, one bit at a time, as data arrive from the delay lines. The results are written back into the lines and registers in a similar manner. Some items are latched, these being the current operation (or "command" in PB 250 parlance) and current operand address. The machine is completely controlled by a central clock. An interesting feature of the central clock is that it was distributable betwixt up to three 250s for multiprocessor implementations!

    The standard input/ output device shipped with the PB 250 was the Friden Flexowriter. This device, which looks like a large electric typewriter, was used as the primary control for the computer as the 250 lacks a full front panel. A wide range of other I/O devices were available as well, including high- speed optical paper tape readers, magnetic tape drives, assorted analogue- to- digital devices, and various sorts of buffer memories.

    In addition to the CPU itself, I also have many of the peripherals which were available at the time, most of which are laboratory interfaces. These include an A/D converter, a "multiverter", a high- speed buffer (with an attached core memory system), and an optical paper tape reader.

    The Packard Bell 250 here appears by arrangement with the Retro- Computing Society of Rhode Island .

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