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From: | Fabrice Bellard |
Subject: | Re: [Qemu-devel] HD Image Size Limits and hdachs |
Date: | Mon, 03 Jan 2005 23:04:24 +0100 |
User-agent: | Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20040913 |
Hi, Happy new year to all :-) Jason Brittain wrote:
Jim C. Brown wrote:One thing is that the maximum number of heads is 256, not 16.That's a good catch, if true. Thanks. But, the doc (the HTML one from CVS HEAD) is very specific about the range being from 1 to 16. I believe you're probably rightand the doc is wrong.
No, the doc is correct. One must distinguish between the Physical CHS (with 16 heads max and this is what -hdachs specifies) and the Logical CHS (with 255 heads max) which is only used by the BIOS to increase the number of sectors that can be addressed. THe logical CHS is specified indirectly when you tell "lba" or "none" as forth argument to -hdachs.
Anyway, nowadays CHS is no longer used when accessing modern hard disks, so it is only a problem for old software using the BIOS to access the hard disk. So _never_ use -hdachs, except if you have to use an old DOS disk image coming from another emulator.
Fabrice.
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