9 track tapes and block sizes

[Paul Koning]

> On Sep 17, 2020, at 2:11 PM, Chuck Guzis via cctalk <cctalk at classiccmp.org> wrote:
> 
> 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.

Even there you might find some oddities.

A RSTS distribution tape, for recent releases, begins with some DOS-11 formatted data, i.e., 14 byte file header and 512 byte data.  That is followed by ANSI labelled data, so 80 byte file labels and data in a VMS-style backupset, 2048 byte blocks I think.

	paul