In message , Paul
writes
wrote:
What is the difference between a regular Format and a Low Level Format?
I have a program to do Low Level Formats. I had a flash drive that
somehow got screwed up. A regular format did
not fix it, but a low level format got it working again.


A partition "Quick Format" assigns a file system to a partition.
It has nothing to do with the workings of the disk drive itself.
A Quick Format writes a FAT or $MFT, writes a file system
header, and that's it. It doesn't check anything.

A partition "Format" without the quick, does a read verify of
every cluster after the same steps as the previous paragraph.
If bad clusters are found, they're added to the $BADCLUS list.
The intention is, with a regular format, to "block" any
bad sectors so they cannot be used. A bad sector is
defined as a sector returning a CRC error, where the
automatic sparing can no longer repair it and keep
the sector in service.

*******

A "low level" format is a disk drive technology, It has
nothing to do with partitions or even OSes. It's something
that happens at the platter level.

Modern drives have a servo pattern recorded at the factory.
The drive is only allowed to write to data sector areas.
So all that a modern drive can do, is "zero" out the data.
It's not allowed to change any other aspects of data content.
As a result, there is no "low level" format on a modern drive.
Even if a command existed in the ATA/ATAPI command set for
it, only the data sector portion could be written.

On an "old" drive, both the sector head and sector data
areas are candidates for writes. During a normal write
operation, only the sector data is written. During
a "low level" format, both the sector head and the
sector data are refreshed. And back in those days,
if you interrupted the "low level" format, the
disk tended to be ruined. When really you should
have been able to start the process over again. It suggests
at the end of the low level format, some info must have
been written to the "critical data" section of the
platter at "track -1". That's also the area where the
drive firmware is kept (when you flash a drive, track -1
gets the information stored there).

A "low level" format can be beneficial to a flaky "old"
drive, but you must not interrupt the process - even
if the software looks like it's frozen :-/ Been there,
and done that.

Paul

In the past few years, I've collected a load old/ancient disks, and used
some of them to 'keep my hand in' doing XP installs on an old clunker
PC. [These never seem to go the same way twice, but that's another
story.]

X-GSmartControl (and other tests) shows that quite a lot of these disks
have a few minor historical errors, so I decided that it might be a good
idea to do a low-level format on some of them (using HDD LLF Low Level
Format Tool). This didn't seem to do any harm to the disks, but on one
type (IIRC, all 160GB Seagate), when I tried to install XP, when it got
to removing the installation disk and rebooting, the reboot came up with
a blue screen showing the message "Unmountable boot volume" (and a lot
more). IIRC, three Seagate disks did the exactly the same, but a couple
of others (Maxtor 40GB, I think) were OK.

So is this just a coincidence, or can a low-level format leave at least
certain types of hard drives looking apparently OK - but unusable for
installing an operating system on?
--
Ian