vax/vms file archival ideas and suggestions

John A. Dundas III dundas at
Thu Oct 19 17:19:14 CDT 2006

At 3:13 PM -0600 10/19/06, Richard wrote:
>In article <a06230902c15d8d43781e@[]>,
>     "John A. Dundas III" <dundas at>  writes:
>>  If on the other hand the files are more important (than being able to
>>  recreate the tape exactly), [...]
>What would require an exact tape image, as opposed to files and their

Tapes where retention of attributes, block sizes, placement, etc., 
are just as important as (maybe more so than) the file contents.  Two 
things come to mind:

1) a simulator (SIMH, Charon, etc.) where you wanted to work with a 
(virtual) tape device.  Pat mentioned booting an OS tape; absolutely.

2) the ability to recreate the tape (either on the same media, TK50 I 
think was this case, or other media 9-track, TK70, etc.).

If I copy files from tape to disk, I lose all blocking information 
(there might be different block sizes on the tape for different 
files).  I won't be able to recreate the tape from the files 
themselves without additional meta information.  Boot tapes often 
(sometimes?) contain boot data/code outside of recognizable file 
headers or marks on the tape.  I believe the early PDP-11 tapes were 
this way.  I can tell you that later PDP-11 (RSTS) tapes are 
multi-format, i.e., the first few (maybe dozen) files are DOS-11 
format, including the boot file, then the rest of the tape is written 
in ANSI format.  IIRC, DEC's Unix-11 V7m contained boot information 
at the front of the tape, then several tar images separated by tape 
marks on the remainder.  A tape image is able to capture this sort of 
information in addition to the file data itself.


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