9 track tapes and block sizes

Chuck Guzis cclist at sydex.com
Thu Sep 17 13:11:15 CDT 2020

On 9/17/20 8:56 AM, Jon Elson via cctalk wrote:

> This is not necessarily true.  Many systems can handle "VBS" (Variable
> Block Sequential) tape files.
> But, yes, fixed block size is more common.

"Hybrid" files are quite common, where all blocks are the same size, but
for the last one.  Or, in the case of some PDP 11 tapes, there's a short
record containing file name, etc. followed by the file data in
uniformly-sized blocks, but for the last one in the file.

Prior to uniform conventions, tape files were anything that the
originator could dream up with regards to block sizes.  Very often, the
correspondence was 1 record = 1 block.

Even the convention of 80 character ANSI tape labels ran afoul of some
36 bit systems, where label records were 81 bytes.


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