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

Guy Sotomayor ggs at shiresoft.com
Mon Apr 18 13:04:35 CDT 2005

On Mon, 2005-04-18 at 11:41 -0600, woodelf wrote:
> Allison wrote:
> >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.  
> >
> >  
> >
> Umm how about real HARD Numbers when talking speeds.

The basic instruction timing on the 11/45, 11/50, 11/55 and 11/70 is
300ns (ie the time it takes for the *fastest* instruction to execute).
There are adders for the different types of memory.  On the 11/45,
11/50, 11/55 there is a 0ns penalty for bipolar.  It gets slower from
there.  I don't have the 11/70 docs in front of me to determine the slow
downs for an 11/70.

One of the other reasons that the 11/45, 11/50, 11/55's are fast when
you put memory in the fastbus is that the fastbus memory is dual ported
so the CPU doesn't slow down when there are other masters on the unibus
(actually they have 2 unibuses but in most applications they are tied

> >When you measure systems, measure the system not just the cpu.
> >  
> >
> Or like everbody does today clock speeds  ...  with a  .3 ns  clock  
> how  fast is
> REAL memory  again?
> Ben alias woodelf

TTFN - Guy

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