PCbanter - View Single Post - What is the difference between a regular Format and a Low Level Format?

**Paul[_32_]** · November 23rd 17, 01:24 AM posted to microsoft.public.windowsxp.general

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