Extracting CDOS and CP/M) files

Fred Cisin cisin at xenosoft.com
Fri Oct 12 11:01:35 CDT 2007


> >Yes.  But MICROS~1 was completely clueless what the risks were and how to
> >deal with them for WRITE caching (what happens if the power goes off, or a
> >disk error occurs before the cached stuff gets written?)

On Fri, 12 Oct 2007, M H Stein wrote:
> Well, in all fairness if the power goes off just before or during a disk write I
> don't see how you could avoid problems without a battery backup or similar.

Two issues:
1) deliberate.  The OS seems to say, "All done", and the user flips the
big red switch.  With write caching, the obvious "all done" signals occur
before the work is done.
2) SMARTDRV rearranged the sequence of writes for more efficiency.  When
power fails, you have a false DIRectory, even though none of the file was
actually written.  Without SMARTDRV, perhaps some of the data was or
wasn't written yet, but the DIRectory will show a 0 length file, since
"closing" the file and writing the updated DIR isn't done until after all
of the data is written.


--
Grumpy Ol' Fred     		cisin at xenosoft.com



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