The VAX is running

Chuck Guzis cclist at
Mon Apr 6 13:18:41 CDT 2009

On 6 Apr 2009 at 13:48, Paul Koning wrote:

> Some of this stuff still makes sense.  You still need external sort to
> sort really large data files, and algorithms that access the external
> files sequentially are still winners even with disk files.

Or bulk core.  Sometime during the 70's, a fellow worker and I were 
teamed to produce a sort that could make efficient use of what was 
then large amounts of ECS.  It was an attempt to salvage the utility 
of the installed ALS hardware, where every installation had at least 
2M words of ECS--and some had 4M.  The volume of data to be sorted, 
however, was much larger than this, necessitating an external sort of 
some kind.

We thought that surely, with a large fast random-access medium, we'd 
be able to improve on traditional tape external sorts.  After a 
couple of weeks of scribbling on whiteboards and headscratching, the 
conclusion was that, no--the traditional external sorts were really 
pretty good even with bulk core.  I recall both Flores and Knuth 
(with the fold-out tape motion charts) were around much of the time.

(For those unfamiliar with CDC architecture, ECS was an external bulk-
core device with significant transfer initialization latency, but 
once going, could transfer a block at full memory bandwidth.  There 
were only two instructions--read and write--to access it)  ECS could 
also be shared by several machines, which for our project, made it 
particularly valuable.)


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