I wanted to benchmark some not-quite-PDP-11 second processors fitted to my BBC Micro, and try to calibrate against a real PDP-11, and that opened a bit of a can of worms… (here are my results - of course, modern implementations outperform the historical ones.)
Wikipedia tells us
In total, around 600,000 PDP-11s of all models were sold, making it one of DEC’s most successful product lines
and
The first officially named version of Unix ran on the PDP-11/20 in 1970
The PDP-11 was sold for over 20 years, with many models and variants were introduced in that time. The PDP-11 FAQ has this to say:
DEC eventually countered with its entry into this market segment - the PDP 11/20 [in June 1970]
Since then, the PDP-11 had 16 to 22 implementations, depending on how you count them, many with variants.
PDP-11 Relative Performance
From a chart in the 1978 "Computer Engineering"
11/03 11/04 11/05 11/20 11/34 11/34c 11/40 11/60 11/45 11/55 11/70
----- ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
Perf(1) 1 2.8 2.5 3.1 3.5 7.3 3.6 27 41 36
core 13
mos 23
Bipolar 41
Whets 26 18 13 20 204 262 57 592 725 671
core 260
mos 335
Bipolar 362
(1) performance is for the basic instruction set relative to the 11/03
From a chart in the 1987 "PDP-11 Systems Handbook"
11/23 11/53 11/73 11/83 11/93
----- ----- ----- ----- -----
CPU F-11 J-11 J-11 J-11 J-11
Microcycle(ns) 300 267 267 222 222
Clock (MHz) ? 15 15 18 18
Performance 0.2 0.5 0.7 1.2 ?
(11/70 = 1)
Cache no no yes yes no
Floating-Pt opt no no yes yes
Coprocessor
The FAQ goes on to do us the favour (in a fixed font) of graphing the performance, sorting by order of introduction:
P r 45 _
e e 40 - -
r l 35 | -
f a 30 | _
o t 25 | -
e i 20 | -
m v 15 _
a e 10
n 9
c t 8
e o 7 - -
6
f 1 5
a 1 4 _ _
c / 3 - _ -
t 0 2
o 3 1 -
r 0_________________M_o_d_e_l_s________________
2 4 4 0 7 5 0 0 3 6 3 2 7 5 8
0 5 0 5 0 5 3 4 4 0 4 3 3 3 3
c
We learn, then, that from the original TTL KA11 CPU through the four-chip LSI and then two-chip single-package F11 and J11 processors, there’s a range of about 14x, and taking into account the cost-reduced low-performance models, a range of nearly 45x.
I also learnt that a company called Mentec made even faster CPUs for the PDP-11, and indeed eventually got the rights to some of the OS flavours too. They seem to have started with overclocked J11s, then made their own (double performance claimed) using TI parts in a microsequenced implementation with an i960 for floating point assist, and finally they offered an ASIC version (80k gates, up to 80% faster.) Notably they only expected to make and sell 1000 of these faster CPUs. Lots of detail in that link about the project:
The total planned effort for the project was 166 person days. The actual project effort took 484 person days. The extra effort put in meant that the calendar finish for the project was completed in 12 months as originally estimated.