7-track tape question

From: Paul Koning <pkoning_at_equallogic.com>
Date: Wed Sep 29 12:51:58 2004

>>>>> "Chris" == Chris Muller <chris.muller_at_mullermedia.com> writes:

 Chris> Hi everybody. This is something a computer geezer like me
 Chris> should know. But I don't.

 Chris> I've read some things that seem to imply that *some* of the
 Chris> oldest drive/formatters did NOT write a longitudinal parity
 Chris> frame at the end of a block. (They did have horizontal parity,
 Chris> of course.)

 Chris> If it's true then a drive reading such tapes would not have an
 Chris> easy way of telling whether frames had been dropped during a
 Chris> read. Does this ring true to anybody out there? Any
 Chris> observations welcome.

It sounded odd to me, so I did some reading.

The IBM 650 (1955) says that it has even longitudinal parity.

On the other hand, the Univac Model 1 (1950 or thereabouts) says that
it has even horizontal parity but not longitudinal parity. But that's
really rather prehistoric and doesn't use regular 1/2 inch mylar tape.

Given that even the 650 has it (as do several CDC machines I checked)
I'm somewhat doubtful about the rumor.

Received on Wed Sep 29 2004 - 12:51:58 BST

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