PDP11/55 sells on Ebay for 5K$ - was it really the fastest 11?

[Jerome H. Fine]

 >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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