[Info-vax] Request description of UFS for VMS person

[Arne Vajhøj]

Bill Gunshannon wrote:
> In article <176uZD2KcidF-pn2-EGCxjRCvkpZd at rikki.tavi.co.uk>,
> 	"Bob Eager" <rde42 at spamcop.net> writes:
>> On Wed, 22 Apr 2009 11:51:40 UTC, billg999 at cs.uofs.edu (Bill Gunshannon)
>> wrote:
>>> In article <gsms0d$dn$3 at naig.caltech.edu>,
>>> 	glen herrmannsfeldt <gah at ugcs.caltech.edu> writes:
>>>> Bill Gunshannon <billg999 at cs.uofs.edu> wrote:
>>>>> Are you saying that the blocks used by a file that has been deleted are
>>>>> not going to be reused?  Assuming a decent file allocation scheme I would
>>>>> expect the freed blocks to be in locations that were likely to be considered
>>>>> prime real estate for the next file that needed space.
>>>> The MS_DOS allocation method seems to be such that the most
>>>> recently allocated blocks are the last to be reused, assuming
>>>> no reboot in the mean time.  As well as I understand it, there
>>>> is a pointer to the last allocated blocks that is incremented
>>>> until it gets to the end, and then starts over from the beginning.
>>> And why does an alocation scheme as bad as this not surprise me?
>>> No wonder we spent so much time de-fraging MSDOS.  :-)
>> It's there to make undelete useful. And that was only on MS-DOS, where 
>> disks were reasonably small.
> 
> Considering that MS never provided an UNDELETE command I doubt that was
> the reason for the allocation scheme they used.  More likely their
> programmers just didn't know any better.

Given that a delete only overwrote the first letter in the
filename in the directory entry so that an undelete utility
only needed to supply the first letter, then your hypothesis
does sound very likely. That type of functionality is not made
by accident.

Arne