Re: Windows 95 (VFAT) file systems?

Michael K. Johnson (
Tue, 17 Oct 1995 16:50:54 -0500

Dan Merillat writes:
> Anyway, why do the drivers like ntfs/hpfs etc allways go readonly?
> If they have the structures etc. done enough to read the dir entrys
> and the files, shouldn't they be able to update them?

Short answer: no
Long answer: Not necessarily.

HPFS I know in particular uses B-trees that are very simple to read,
and much harder to update. I don't know of the other challenges,
although I assume they exist.

In general, being able to parse a data structure doesn't imply
knowledge of the invariants used while creating it. As an example
from a different domain, as I'm working on my scanner driver, I have
not yet been able (even with documentation) to get it to scan correctly.
However, if I had a SCSI sniffer between my box and the scanner, I would
be able to understand everything going on between the two.
Understanding what is going on parallels readonly, being able
to scan parallels read-write.

Does that help?

> Oh well. Just a personal pet peeve.

Short answer: So fix it...

Long answer: Do you really think that the people writing the
filesystems would stop at read-only if it were actually only
a little bit more work to add read-write, or if they had the
info right there, or if they trusted their knowledge of the
data structures enough? The filesystem authors I know really
aren't trying to annoy people...