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From: cgordon@vpnet.chi.il.us (gordon hlavenka)
Newsgroups: comp.os.msdos.programmer
Subject: Re: What is low-level/high-level FORMAT?
Message-ID: <1991Jan21.022114.23765@vpnet.chi.il.us>
Date: 21 Jan 91 02:21:14 GMT
References: <61737@brunix.UUCP> <12052@ccicpg.UUCP>
Organization: Vpnet Public Access
Lines: 26

I am curious as to some of the details of the MS-DOS "High-level" format.  If
the LL format writes sectors, gaps, etc. and the HL format "builds the file
system structures", why does the DOS HL format not complete in only a few sec-
onds?

DOS accesses the disk in clusters of (typically) 4 sectors per cluster.  The
DOS file system "structures" for a blank (but formatted) disk take up only a
few sectors:  0 (boot sector), two FATs (approx 30-50 sectors/FAT), and a
root directory (one cluster).  Yet a DOS HL format takes several minutes and
appears to make some kind of access to every sector on the disk.

Is there some special "DOS Sector Header" which gets added?  I know that DOS
will mark clusters containing bad sectors during a format, so there is at least
some kind of surface validation going on.  Is this the only reason for access-
ing the whole disk?

Norton 4.5 has a "Quick Format" which only writes new FAT/root directory data.
Is there any reason why this couldn't be used to install the DOS file system
on a (non-bootable) LL-formatted hard drive?



-- 
-----------------------------------------------------
Gordon S. Hlavenka            cgordon@vpnet.chi.il.us
Disclaimer:                Yeah, I said it.  So what?