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

Eric Smith eric at brouhaha.com
Mon Apr 18 02:59:00 CDT 2005


Heinz wrote about the PDP-11/55:
> claimed that it was the fastest PDP11 of
> the blinkenlights
> machines made by DEC.. Is that true?

With bipolar memory, the 11/45 or 11/55 are definitely the fastest
DEC machines with "real" front panels.

>  I expected  an 11/70 to be instruction for instruction faster

No.  The cache was roughly the same speed as the bipolar memory of
the 11/45 or 11/55, but main memory was slower.  And access to Unibus
was slower.

> How about compared to a 11/70 with a PEP70 instead of factory memory and
> cache?

With PEP70 (replaces DEC main memory) it should be faster.  With PEP70 and
HC4x Hypercache (replaces DEC cache) it should be much faster.

With QED95, even faster yet.  But is it still an 11/70 at that point?

Eric




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