PDP-1 as minicomputer [was RE: OT - sort of]

This is probably one of the most problematic questions I try to answer, far too often: why is X a minicomputer and not something else? I think of a minicomputer as a machine designed to not require an operator staff, designed for direct interaction between the user and the computer (rather than batch operation), and designed for a *relatively* small resource footprint (the PDP-1 required a LOT less resources than a 7090). There is a lot of fuzz around all of these factors. Is a VAX-11 a minicomputer? It takes three-phase power and was intended to serve as a large timeshared system. There is a mechanism to run batch jobs. There was a role defined for the "system manager" who maintained various aspects of the OS environment. However, at the same time IBM's product line consisted of machines that still cost ten times as much, could NOT be meaningfully maintained without an operations staff and were fundamentally designed for batch processing. The VAX-11 was "mini" by comparison. It is feasible for one person to operate and use a VAX; the question in the context of a VAX-11 is an economic one, not a question of operational overhead. Consider that when IBM transistorized the 709, they did NOT build a smaller computer based on the increased functional density of the transistor. They built a large computer with more capability. In contrast, the PDP-1 was intended to be small enough that it wasn't a perceived economic absurdity for it to be used single-user. For counterpoint, the PDP-10 was never intended to be anything other than a mainframe-class machine. Its capabilities, capacity and footprint all served as direct competition to System/360. So DEC != minicomputer, although they were the leading manufacturer of that class of machine for many years - indeed, until the microcomputer began overshadowing the mini. This is an interesting question, and I hope we can have some meaningful dialogue about it - and maybe even stay on topic. :-) -- Ian