Lyle Bickley wrote:
>Copyright 1978 by Digital Equipment Corporation
>Page 408
>--------
>Model Basic Instructions Floating Point
> Inst. per second* Inst. per second
>-------------------------------------------
>11/70 36 671
>11/55 41 725
>* Relative to 11/03
>No brainer - the 11/55 wins hands down.
>
Sorry, while for those metric the 55 was a tad faster, for IO the 11/70 was
massively faster. At that time to do large arrays of data you needed lots
of fast IO to disks as you could only works with part of an array at any
time due too addressing limitations of the PDP11.
When you measure systems, measure the system not just the cpu.
System performance is application dependent.
If you were going to do FORTRAN FP, the 11/55 would be a good choice. This
specific 11/55 it was used as part of a flight simulator - a perfect
application for the high performance (CPU) 11/55.
If you were running a RSTS/E shop with lots of I/O (as I did many years ago),
your choice would have been an 11/70 - for it's massbus I/O capabilities,
good integer/FP performance, and memory capacity.
So saying it is the "fastest blinkenlights" system is certainly valid in the
context of its application - and in the manner that "Computer Engineering"
documented its performance.
Jerome Fine replies:
Does anyone have any benchmarks programs and
results (so they can be used with other
configurations) that have been run on various
PDP-11 systems? It would be helpful if the
non-DEC CPUs and emulators could be included.
If possible, benchmarks for RT-11 are required.
Source code would be satisfactory.
As far as I know, the PDP-11/93 (or the PDP-11/94)
was supposed to be the fastest DEC PDP-11 system.
But at least three other hardware replacements,
including QED and Mentec models were available.
When emulators are included, I understand that E11
is the fastest system (when run on the fastest P4)
being able to achieve at least 30 times a PDP-11/93
and perhaps up to 75 or even 100 times a PDP-11/93.
I have run E11 on a 750 MHz Pentium III and speeds
of about 15 times a PDP-11/93 were achieved. While
I hoped that a 3 GHz P4 would be 4 times as fast,
I was a bit disappointed with the limited testing
I have been able to attempt - I seem to find that
the P4 is only about 2.5 times that Pentium III when
I run an RT-11 benchmark under E11 under Win98SE.
One of the reasons that E11 is so fast is that for
benchmarks which require only a small capacity of
disk space (less than 1 GByte), the ability of the
operating system to cache the disk space used could
make the I/O portion of the benchmark even faster
than the CPU portion when the Pentium system has
sufficient RAM.
Sincerely yours,
Jerome Fine
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