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

[Lyle Bickley]

On Monday 18 April 2005 07:05, Allison wrote:
--snip--
> >> Read "Computer Engineering" (Gorden Bell, J. Craig Mudge, John E.
> >
> >McNamara),
> >
> >> 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.

Cheers,
Lyle  
-- 
Lyle Bickley
Bickley Consulting West Inc.
http://bickleywest.com
"Black holes are where God is dividing by zero"