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

[Tom Uban]

At 11:04 AM 4/18/2005 -0700, Guy Sotomayor wrote:

>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
>together).

I believe that speed of access to the Unibus on the 11/45 (et al) is also
quite a bit faster than that on the 11/70, although I don't recall the
reasons.

--tom


> >
> > >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