[Info-vax] Backup TK50 tapes

[Paul Sture]

In article <kgj03k$2ke$1 at Iltempo.Update.UU.SE>,
 Johnny Billquist <bqt at softjar.se> wrote:

> On 2013-02-26 18:35, Paul Sture wrote:
> > In article <kgh0n3$gjv$1 at Iltempo.Update.UU.SE>,
> >   Johnny Billquist <bqt at softjar.se> wrote:
>>
> > My memory isn't shining here, but I'll agree with other posters that
> > tape to disk to tape wasn't the same as tape direct to tape.  I also did
> > what another poster mentioned and experimented with the ordering of
> > files on TU58s to get faster boot times.
> 
> TU58... Brrr.... The TK50 was a huge improvement...
> Although the concept of the TU58 is nice.

The concept was nice, but the execution times weren't :-)
 
> Anyway, the problem with bootable tapes, at least on a PDP-11, is that 
> your tape starts with a boot block. That block is read into memory, and 
> the boot rom jumps into the code read in. This boot block on the tape is 
> outside of what is visible as files on an ANSI-labelled tape. So you 
> cannot see, or access this block except by doing low level reads from 
> the tape. Any tool like COPY is unable to see or access this data.
> 
> The boot block in turn have enough intelligence to actually start 
> accessing things in a more structured way. The boot roms just assumes 
> that the first or second block on the tape is the boot block.

Understood.

-- 
Paul Sture