I would have to concur. I have a physical 11/05. The 11/05 (same CPU as
the 11/10) and it is nowhere near as capable as an 11/03. For a while
there DEC had a tendency to release two new machines at a time. One
would out perform the previous flagship processor, probably not costing
too much more. The other would be comparable with the previous flagship
processor but at a lower cost. The 11/05 was the similar capability
lower cost follow on to the 11/20.
Comparing the 11/05 is slower than the 11/03 and lacking a bunch of
useful instructions. The 11/05 is totally devoid of any memory
management - 64K address space is all you get.
You could not configure 64K, of course because of the reserved address
space. Mine has 32K, which I suppose is a typical large configuration.
Core memory was expensive. I suppose one could have added a 16K board
and had 48K but justifying the expense would have been difficult.
On 7/7/2012 3:14 AM, Göran Åhling wrote:
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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