IBM 5120 at the local thrift store

I wrote: Doug replied: The IBM numbers are 'Type' numbers. For instance, for the Type 729 tape drives, there are Model I, II, III, etc. For the Type 360 computer, there were initially Models 30, 40, etc. The IBM AT was Type 5170, but had many Models, such as the famous 339. However, for computers, each box generally had its own Type number. When you talk about an IBM Type 7090 Data Processing System, that's actually just the type of the main processor. The memory, the I/O channels, even the control console each have their own type number, from the same name space. Even a 360/30 has a Type number for its CPU, although I don't recall offhand what it was. They've definitely had more than 10,000 Types, and probably more than 100,000 Models. But not every Type is a "computer".