Description
MOBIDIC's design goal was the real time operation of its input/output system. A typical use for MOBIDIC would be to collate all the messages flowing through an input to different tape outputs based on a field in the data. The tapes could then be removed and the messages printed on an offline printer. For instance, a large supply depot might have numerous warehouses for different sorts of materials; MOBIDIC could route incoming requests by examining the part number and then sending that message to a particular tape. All of the output on that tape would then be printed and sent to the associated warehouse. MOBIDIC replaced many manual steps; it performed the collation lookup, sorting the data, and collecting all the printed messages for delivery.
MOBIDIC was a 36-bit binary machine, a common word size for early computers. The system used 36-bit data throughout, but stored it as 40-bit values to add additional sign and parity bits, and two spares. This allowed it to store the full range from -(1 - 2−36) to +(1 - 2−36). Machines were normally equipped with two parallel banks of core memory with 4096 words each, but was expandable to seven banks maximum. It could support up to 63 tape drives, punch tape input and output, as well as a Flexowriter. One connection could also be dedicated to sending data to another MOBIDIC system. The tape drives used one of the spare bits in the 40-bit word as a STOP indicator.
Most of the 52 instructions were in the one-address format, collecting into an accumulator, but a small number (load, move, etc.) were in two-address format. There were 15 arithmetic, 8 transfer (memory), 17 logic, 3 sense and 9 input-output instructions. An add required 16 microseconds, a multiply or divide 86, these slow times a side effect of its serial operation.
MOBIDIC's CPU and I/O systems were housed in a 30 foot (10 meter) van. The machine required 29.76 Kw of power, which was supplied from a second, smaller, van containing a generator set.
The dual-CPU MOBIDIC B (only one was produced) included three additional general instructions, as well as nine new instructions for supporting subroutines. The CPU's were independent, but shared a single main memory consisting of 8,192 words of core. In a sample use, one of the CPUs would be used to import data, handing off data via shared memory to the second for output. Although the machine's speed was slower overall (adds were 42 μsec), throughput could be greatly improved. If one of the machines failed, the program could be re-started on the remaining CPU, running both sides of the I/O task with reduced throughput.
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