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From: Ian Jackson 
Newsgroups: microsoft.public.windowsxp.general
Subject: Re: What is the difference between a regular Format and a Low Level
Format?
Date: Thu, 23 Nov 2017 09:27:05 +0000
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In message , Paul  
writes
>james{at}nospam.com 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
--- Platinum Xpress/Win/WINServer v3.1