From: NoEmailAds AT execpc DOT com (Chris Giese)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Raw disk access
Date: Thu, 14 Nov 2002 03:03:59 GMT
Organization: PROPULSION GROUP
References: <aqrp5n$2pn4$1 AT gavrilo DOT mtu DOT ru>
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Michail Pishchagin <mailfrom AT mail DOT ru> wrote:

>Is it okay to use _bios_disk function for reading? Does it support reading
>sectors beyound 1024 cylinder at least on modern BIOSes?

_bios_disk() and biosdisk() use INT 13h AH=02h. All three functions
have the same limitations. You can access a disk up to 8 Gbytes if
the BIOS supports CHS translation, but only ~500 Mbytes if not
(this is the same thing as the 1024 cylinder limit).

If you need to access disks larger than 8 Gbytes, get this file:
        http://my.execpc.com/~geezer/osd/disks/diskio.zip
and look at function lba_biosdisk() in file DJGPP.C
To use this LBA function, both the drive and the BIOS must support LBA.

>And is there some elegant way to determine how many physical hard drives are
>installed on computer?

The byte at address 0475h contains the number of hard drives
detected by the BIOS:
	num_hds = _farpeekb(_dos_ds, 0x475);

The number of floppy drives detected by the BIOS can be had
from the Installed Equipment word at address 0410h:
	num_fds = _farpeekw(_dos_ds, 0x410);
	if(num_fds & 0x0001)
		num_fds = ((num_fds / 64) & 3) + 1;
	else
		num_fds = 0;

-- 
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