ComputerVision CADDStation tapes now available (sorta)

Chuck Guzis cclist at sydex.com
Wed Aug 9 15:07:55 CDT 2006


On 8/9/2006 at 9:51 PM Nico de Jong wrote:

>The standard for IBM labelled tapes is that there is 1 tapemark between
>files, and 2 tapemarks to indicate that the last file has been read.
>As there are two tapemarks between files, how can you then detect
>end-of-data ? 3 or 4 tapemarks ?

Depends on the vendor.  Some used more than 2 filemarks.  From a hardware
(and software) point of view, there's nothing to prevent it.  If you think
about it, it makes sense.  A corrupted filemark will cause a tape drive to
skip one more record than requested.  A double filemark adds a bit of
redundancy.

Particularly in tapes, IBM's practices weren't universal; nor, for that
matter did everyone adhere to ANSI standards.  You can probably still find
plenty of old tapes without labels, with strange block sizes, in mixed
densities, etc.  200 bpi 7-track EVEN parity tapes were even used at one
time (There was no way to write a binary zero character).   Tape conversion
between vendors used to be a big deal 30+ years ago.

Chuck





More information about the cctech mailing list