#Unformatting a disk
14 messages in this thread
Thank you for your help, but I felt sure that the Amiga might have some program
available, such as Norton Commander for the IBM, that might help. If per chance
I find something like that I will let you know.
Gabrielle
Gabrielle,
Nothing will recover data from a formatted disk on the Amiga or on an
IBM. What the Norton utilities can do is recover a file that has been deleted.
On a PC, when you delete a file, all you do is mark the directory entry for
that file to show it's been deleted and free up the sectors used by that file
by showing them as unused. That doesn't change any of the actual data until
you write a new file to the disk, then the data from your old file might be
overwritten.
When you format a disk, you write over every sector…any data that was
there is changed to all 0's. Since that data has now all been changed, there
is no way to know what that data used to be…it simply doesn't exist any more.
On the Amiga, it's the same thing. If you've only deleted a file, then
it can be recovered IF you haven't written any new files to the disk since you
deleted the file you want to recover. The program DiskSalv (DSKSLV.ARC in DL
9) will do this for you and I also believe that Disk Doctor (comes with the
Amiga) can recover lost files.
However, if you formatted the disk, there is now way to recover the
data because there is no data left to recover.
Don
I don't remember the details, but I'm fairly sure Gabrielle is correct in what
he says about "unformatting" on the IBM. The reason it works is that the disk
doesn't truly get formatted in the sense of truly overwriting everything in the
world unless you use the low-level formatting utility (I forget the IBM
terminology, but I think you need a diagnostic disk to do it). The customary
DOS FORMAT command still leaves enough when you do it to a hard disk that you
really can "un-format"! For similar reasons if you have a sufficiently badly
trashed IBM hard disk FORMAT isn't sufficient to "format" it again.
Douglas,
Nope…the standard FORMAT command under MS-DOS will wipe a disk clean,
all data sectors are zeroed. There is a Norton Fast Format command thou, and
all that does is zero the directory sectors and show all sectors as available.
That's another whole thing, essentialy all that does is delete all files.
Under MS-DOS, if you use the standard FORMAT command, either with a
Hard Disk or a floppy…all data is permanently lost.
Don
Don, in fact one _can_ unformat an IBM disk. Mace utilities allow one to do
this. Data is _not_ written to the entire disk during a standard MS-DOS
format, only timing pips.
Tom,
I'm sorry, but I've looked at sectors both before and after a format
under MS-DOS and the data is _gone_. However, just to make sure, I just did it
again about 30 seconds ago. Took a sector editor and looked at a sector, it
had data in it, quite readable as the sector I happen to pick was the middle of
a database file. I then formatted the disk, using a normal format command,
nothing special. I then went back and re-read that same sector. It was now
all 0xF6 characters. Definately not what was on the disk before formatting.
I have done the exact same thing on a Hard Disk, just to satisfy my
curiosity, unfortunate, I'm not that curious now to run a backup, format and
restore of the HD…but I can tell you the results were the same.
Don
p.s. BTW, just to keep everybody happy…I looked at all the sectors beyond the
system sectors (FAT tables, etc.) and they were all 0xF6 for every data byte.
I'm not trying to be argumenative, but format does destroy the data under both
AmigaDOS and MS-DOS.
Tom,
I see from other messges that apparently on a HD, MS-DOS may not write
to the sectors themselves during the format. I know I've looked at HD sectors
before and after a format and they were zeroed…but that was on an older
version of DOS. We were doing some tests to check on sector size and the like
and were doing formats and then going back in and looking at the sectors to see
what was being written.
In any event, in the next few days or so…I might as well bite the
bullet and backup and re-format my HD at work. It's getting fragmented anyway
and I'll re-run the test. I'm using 3.2 there (and here also) so until I run
the test…let's just say "let's wait and see".
Don
The name of one utility which claims to be able to recover data from an
accidental format is Disk Technician.
Tom,
There has obviously been some changes, I went and formatted an HD under
MS-DOS and sure enough, as you folks have been saying, the data is still there.
This is not true for floppies, but for a HD, under the latest versions of
MS-DOS it is.
With that in mind, then yes, I do see that it would be possible to
recover data from an accidently formatted MS-DOS HD.
Now, as to what happens with an Amiga HD, that I haven't checked out
yet.
Don
Don,
The Amiga formats a hard drive by writing new data to it a cylinder at a time
and reading it back to check that it was written out.
I say this with some reservation, because it is certainly possible to write a
hard disk driver that does something other than what Amigados expects. This
might tend to cause problems later, though I can't see that it would be a big
thing to do.
I wonder… what is the general feeling on this? Would the average hard drive
owner rather have a FORMAT command that can be recovered from? If so, I would
certainly write it into my driver, and probably provide a utility to recover.
Regards, Larry.
Larry,
Good question…in doing my test with the MS-DOS HD, I went and made a
backup. I then formatted the drive and attempted a restore. The backup was
bad!!! I now have to go re-construct the HD and that's a pain.
But, then again…since the backup started to write to the HD (of the
23 disks in the backup set…5 were bad), I couldn't have recovered anyway so
I'd say, let a format be a format…write 0's (or whatever) to the disk and
read them back to verify the data was properly written.
Don
Larry,
MS-Dos world divides things into 'Format' and 'Low-level Format.' The former
is done with the MS-DOS Format command. The later is done with the utility
diskette supplied by the disk drive manufacturer, or by issuing (machine
language) commands directly to the controller via DEBUG.
As a manager, I would _far_ prefer a 'Format' that can be recovered from to
one that writes and reads zeroes, coupled with a low-level zeroer which is Hard
To Use.
People can select Initialize from the Workbench menu. That's no place for a
low level format program to launch!
Thomas,
In the Amiga's case, it is strictly up to the author of the driver as to what
happens when it receives a format command. Some of the possibilities are:
1. Format on a high level basis by wiping the data.
2. Format by 'faking out' the format program and not writing anything except by
'write command'. (This allows the format program to set up the DOS block, root
block, and bitmap)
3. Format both low level and high level.
Each method has its advantages, and I really don't know what most would prefer.
Regards, Larry.