Date: Thu, 24 Jul 2003 20:25:06 +0400 From: Yar Tikhiy <yar@freebsd.org> To: Josef Karthauser <joe@freebsd.org> Cc: fs@freebsd.org Subject: Re: [Off topic] Trashed NT disk Message-ID: <20030724162506.GA54954@comp.chem.msu.su> In-Reply-To: <20030724155818.GA50385@comp.chem.msu.su> References: <20030723175448.GA33453@genius.tao.org.uk> <20030724155818.GA50385@comp.chem.msu.su>
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On Thu, Jul 24, 2003 at 07:58:18PM +0400, Yar Tikhiy wrote: > > On the dmesg vs. BIOS issue: To a programmer's view, a modern drive > is just a linear array of sectors. However, software has stuck to > the cylinder/head/sector (CHS) way of addressing. So drives report > some fictitious geometry, with traditional IDE values for the number > of heads and sectors per track at 16 (or perhaps 15) and 63, > correspondingly. BTW, the nature of these numbers seems to be as follows: 16 heads is a limitation of the ATA (IDE) protocol. 63 sectors is a limitation of the old BIOS interface. > Now BIOS seems to be the only consumer of the old, CHS, fields in > MBR -- the rest of software uses the logical offset and size fields > that were introduced to the MBR format at some moment. That's why > it's the BIOS geometry that you should care about when partitioning > a drive. After some reading, I'm afraid that the "logical" (or "relative") fields were present in the original MBR format. However they had been miscalculated by MS-DOS fdisk and not used by anything else until drives grew large enough to really reqire them for partitioning. -- Yar
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