external sorting with 9-track tapes

[Chuck Guzis]

On 4/10/2006 at 11:51 AM jim stephens wrote:

>tape sorts make IBM 3420's make the strangest noises you might ever hope 
>to hear out of a drive.  Most of the action is not visible, but is in very
high 
>frequency vibrations in the vacuum columns, and some unusual motion in the
tape 
>loops in the columns.

Sorting (and its cousin, merging) used to be a big deal in the data
processing world.  Many hours were spent working with oscillating or
polyphase merge sorts.  I remember when I was told that I could use DISK to
sort my data  (we had a large roomfull of CDC 844s).  My reaction was "wow,
with random access to any point a file, I can really make a sort fly!"
When it got down to paper, however, it turned out that the old methods that
used tape also worked very well on disk.  I remember how disappointed I
was--sort of like being told that there was no Santa Claus.

For those of you unaccustomed to tape sorts and wondering how that could
possibly be; remember that we used multiple tape drives and while a tape
might be rewinding, data was still being written and read to other tapes.
You might think that you'd save a lot of time by not having to rewind a
disk, but it really doesn't matter. 

Cheers,
Chuck