[Info-vax] TK50 - this is annoying...

[George Cornelius]

glen herrmannsfeldt wrote:


> IBM 9-track tape drives, farther back than I can remember, could
> read backwards. At least for S/360 and successors, when you read
> backwards the buffer is filled up from the end to the start,
> such that the bits and bytes end up the right way. If the block
> is shorter then the buffer, it will be at the end instead of
> the beginning, though.

Yes - the selector (and multiplexor?) channels had to run backwards.
 
> There are external sort algorithms optimized for tapes that can
> read backwards. It saves a rewind between writing and reading
> the data back in. The usual algorithms sort blocks of data
> that fit into memory, then write them to tape. It then doesn't
> matter what order they come back in. For merge, you have to
> be a little more careful with the data.

SyncSort - the first software patent ever issued. This was a
_big deal_ because no one knew whether software should be patented
or copyrighted.  The justification for issuing the patent: it was
the _physical process_ which you were being allowed to patent,
not the program, which was considered perhaps unpatentable because
it was thought to be equivalent to an (unpatentable) mathematical
equation.

George Cornelius