Editing MOBIDIC (section)

==Description==
[[File:Sylvania MOBIDIC model (2585216399).jpg|thumb|Model on display in the [[Computer History Museum]]]]
MOBIDIC's design goal was the [[real-time computing|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.<ref name=w50>Weik, pg. 0650</ref> This allowed it to store the full range from -(1 - 2<sup>−36</sup>) to +(1 - 2<sup>−36</sup>). Machines were normally equipped with two parallel banks of [[core memory]] with 4096 words each, but was expandable to seven banks maximum.<ref name=w51>Weik, pg. 0651</ref> It could support up to 63 [[tape drive]]s, [[punch tape]] input and output, as well as a [[Friden Flexowriter|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 (computing)|accumulator]], but a small number (load, move, etc.) were in two-address format. There were 15 arithmetic, eight transfer (memory), 17 logic, three sense and nine input-output instructions.<ref name=w50/> An add required 16 microseconds, a multiply or divide 86, these slow times a side effect of its [[Serial computer|serial operation]].<ref name=w51/>

MOBIDIC's CPU and I/O systems were housed in a 30-foot (10 meters) van. The machine required 29.76&nbsp;kW of power, which was supplied from a second, smaller, van containing a generator set. Two other vans contained auxiliary EAM equipment and a repair shop. All four vans were backed up; two to a side, to a raised wooden platform with steps on one end. As this was the Cold War era, in case of enemy attack, everything could be moved instead of having to be abandoned and destroyed.<ref name=w52>Weik, pg. 0652</ref>

The dual-CPU MOBIDIC B (only one was produced) included three additional general instructions, as well as nine new instructions for supporting subroutines. The CPUs 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&nbsp;μs), throughput could be greatly improved. If one of the machines failed, the program could be restarted on the remaining CPU, running both sides of the I/O task with reduced throughput.<ref name=w54>Weik, pg. 0654</ref>