[Info-vax] Backup TK50 tapes

[Stephen Hoffman]

On 2013-02-27 03:10:49 +0000, David Froble said:

> I'm going to take a guess here and state that the 32K limit was in VMS. 
>   Specifically, there is a VMS limit of 32K for string lengths.  The 
> string descriptors use 16 bits to specify the string size.  I'm going 
> to guess that string descriptors might have been used to specify 
> buffers. 16 bit length, 32 bit address ...

There was a limit of 32 KiB for string descriptors, and that old limit 
is still present on OpenVMS VAX systems.  The limit was lifted on the 
64-bit systems at OpenVMS Alpha V7.0, and on OpenVMS I64 systems.   
Quick C example of 64-bit string descriptors: 
<http://labs.hoffmanlabs.com/node/787>

(Whether it was the size of the tape controller hardware registers or 
maybe ANSI tape specs or the old 32-bit descriptors that led to the 
transfer size limit or a general "32-bits is good enough" moment, 
donno.  Don't really care all that much about the origin of the limit, 
either, as I'm not booting off tapes, not copying tapes, and have 
relegated the remaining tapes to long-term archival-storage purposes, 
for those cases where there are still tape loaders or tape libraries 
around.  I'll leave that to the retronauts and retrohistorians to 
debate.)


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