Well, I'd used the word "Weakest" to describe this aspect of a computer...
Without reading any PDP-11 architecture handbook (today), I'd like to claim the initial design, the 11/20, to have the weakest architecture within the PDP-11 family, it was released in 1970.
Just as all (almost) PDP:s the customer would order a CPU, and separately order as much or little of memory that was regarded "neccesary" for every task... 11/20 had a max. of 56 kB (28 kW), as the design has 16 bits of adressing (=64 kB), but 8 kB are reserved for I/O devices.
Exactely how little memory that would be enough to run an OS, Teco and an async port, I can't judge, but running an emulator, like SIMH, would alow for testing of this. The 11/20 was sold along with core memory, so a fair core memory card size for the minimum system would be elegant...
The instruction set of a PDP-11 was slightly extended with EIS for modells comming just a few years later, as several options (floating point support, commersial calculations support, memory management for 18 or 22 bits of address-space...)
But, as Johnny says, the LSI-11, aka PDP11-03, beeing the first LSI-design from DEC, released in 1975 with the new LSI-bus (aka Q-bus) is always remembered as the slowest PDP of all times, even though the architecture might be slightly improved over 11/20!
If you would like a running real physical system, the 11/03 would by far be the easier to get hold of, get running, and keep running. The 11/20 would typically need 2 pcs of 19" wide, 72" high racks... For emulation, this is however not an issue!
/Göran On 2012-07-06 21:04, Richard wrote:
When I say "small", I'm referring to computational capacity, not physical dimensions.
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