> From:    "Paul J. Traynor" <[log in to unmask]>
>
> Hi,
>
> Could someone answer the following questions please.
>
> 1.  what is the purpose of a low level format?

Back in the days of MFM (Modified Frequency Modulation) and RLL (Run Length
Limited) encoded hard drives, things like stepper motors, thermal
expansion, gravity (whether the spin axis is up-and-down or sideways),
and normal wear-and-tear caused the positions of the magnetic bits on the
disk to shift relative to the placement of the heads.  By waiting until the
system had reached its normal operating temperature (or at least 20 minutes),
and was in its usual orientation, a low-level format would renew the
complete disk format, so that the bit positions were as close as possible
(relative to head positions) to a new drive.  Just like a new drive, there is
NO information stored on the drive.  (Ok, if you have the resources of
somebody like the CIA, you might be able to recover something...).

If you have a MFM/RLL drive (identifiable because it has both a 20-pin and a
34-pin edgecard connector and cables - or also ESDI?), you can download the
appropriate software from the manufacturer for that model of drive.

There was also usually a generic low-level format built-into the hard
disk controller chip, which could be activated from DEBUG.

DO NOT ATTEMPT THIS if you have an IDE/EIDE drive.  Most are now low-level
format-proof - but some are not.  If you succeed in reformatting the entire
disk, including the factory-installed guide tracks that define where all the
cylinders fall on the other surfaces, you will have to send it back to be
re-installed at the factory, as only the factory has the precision
equipment to do the job.

If you use the manufacturer's "low level format" on an IDE/EIDE drive,
make sure that you have their "blessing" - some manufacturers consider
this to void their warranty if it goes wrong, or if you accidentally use
the wrong software.  Their software will not affect the guide tracks,
just zero the rest of the drive.

Because all the platters on an IDE drive "grow" the same amount as the drive
warms up, and the heads all droop the same amount due to gravity, this
dynamic method of locating cylinders/tracks is better.  So is the
continuously variable "voice coil" circuitry which precisely follows the
guide tracks to define cylinders.

> 2.  In what situations is such a technique required?.

If a hard drive has been magnetically damaged (say a bad controller mis-wrote
all over it), or you want to make sure the buyer of the drive can't just
UNDELETE your tax files, or nothing else has been able to remove a nasty
virus.  If you plan on re-orienting an old (stepper motor) hard drive by
standing the case on its side, or moving it to a new case in a different
orientation.

It may also be useful in recovering "bad" sectors if the damage was only
magnetic (Say half-a-dozen bad sectors are diagnosed after some of many
power outages.)  There is a possibility of recovering a sector with
slight physical damage (manufacturing blemish, "gentle" head crash),
recording vital data onto it, and then having it go "bad", losing the
data.  If any sectors are identified as "bad" on a printed list from the
manufacturer, they should be entered as "bad" manually, even if the low
level format thinks they are "good".  The manufacturer has more sensitive
means of testing for dubious sectors.

> 3.  If special software is needed are there any freeware or shareware
> utilities to be found on the net?.

Usually, the drive manufacturer's software is freely downloadable.  DEBUG
is already in DOS, but can be dangerous if used improperly. (If you REALLY
want to know how, e-mail me off-list.)  The names ONTRACK, SPINRITE, and
DISKMANAGER also come to mind...

> Many thanks in advance,
>
> Paul Traynor

Have fun with it - but be patient!  Some large drives can take more than 24
hours to complete (although you should be able to follow the progress of the
operation.)

Boyd Ramsay

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