Chuck Guzis wrote: One more category springs to mind--5xx would be printers (e.g. 501 and 512). Maybe I;m trying to forget about what it was like having a machine gun on one side (501 drum printer) and a screaming banshee (512 train printer) on the other side. 8xx also includes drum storage. ------------------------------------------------------------------------ To add a little more: 1XX was test equipment; 3XX was paper tape equipment; 7XX was interconnect gear. Later the numbers were changed to an elaborate code that used 2 Alphanumerics a dash, 3 more alpha numerics. This was later modified to include another dash and alphanumeric. For example, a disk drive might be: BJ-3A4-C. There is a model decoder somewhere on bitsavers. And there was a whole family of unique specially designed peripherals called SPAM boxes = Special Purpose Alogrithm Machines. These were usually all electronic. Most were used in the oil industry; for example strip recorders/readers for seismic data. One I worked on a lot when in Houston, would add up all the one bits in a large field of data. For some applications, the petrol companies loved it. Inital telecommunication products started here then evolved into their own families. Chuck, I'll swap you for the time I was at CERN working on 627 (one inch) tape drives and some idiot rewound 24 of them at the same time. It was a gag they pulled on new operators. It could take an hour before you could hear people talk again. Billy Pettit