From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.33) id 1BljQB-0004or-Mi for qemu-devel@nongnu.org; Sat, 17 Jul 2004 03:15:47 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.33) id 1BljQ9-0004oM-Np for qemu-devel@nongnu.org; Sat, 17 Jul 2004 03:15:47 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.33) id 1BljQ9-0004oJ-IL for qemu-devel@nongnu.org; Sat, 17 Jul 2004 03:15:45 -0400 Received: from [62.253.162.41] (helo=mta01-svc.ntlworld.com) by monty-python.gnu.org with esmtp (Exim 4.34) id 1BljNG-0001ky-JK for qemu-devel@nongnu.org; Sat, 17 Jul 2004 03:12:46 -0400 Received: from [10.10.10.100] ([81.107.87.144]) by mta01-svc.ntlworld.com (InterMail vM.4.01.03.37 201-229-121-137-20020806) with ESMTP id <20040717071211.UMUL9394.mta01-svc.ntlworld.com@[10.10.10.100]> for ; Sat, 17 Jul 2004 08:12:11 +0100 Subject: Re: [Qemu-devel] BIOS behaves different as real BIOS From: Antony T Curtis In-Reply-To: References: Content-Type: text/plain Message-Id: <1090048364.21480.6.camel@pcgem.rdg.cyberkinetica.com> Mime-Version: 1.0 Date: Sat, 17 Jul 2004 08:12:44 +0100 Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org On Sat, 2004-07-17 at 07:01, Natalia Portillo wrote: > Hi! > > I tried to boot an old operating system from qemu and I get a message from > BIOS saying that tbe floppy is not bootable (literally: "FATAL: Not a > bootable disk"). > > I think that this is because the BIOS searches for the 0x55AA signature on > last two bytes of first sector of disk. > As far as I remember, this signature was introduced very lately and as far > as I tested on my real systems, this signature is not really searched at > boot time, and every DOS before 3.0 doesn't have it (it is used also by > later DOSes and Windows to identify a FAT filesystem), at least on floppies > (I think that on hard disks it is also ignored, but never tested -0x55AA is > also used to identify Intel partition scheme, aka MBR-). I remember looking at the IBM PC/XT BIOS source and seeing it, and when I used to play with putting my own messages in the boot sector, It had to be there. This was around 15 years ago. The old IBM PC/XT would boot into ROM Cassette BASIC if it did not find the signature. It is possible that the original IBM PC did not have the check but by the time the PC/XT came out, it did. The model of the PC/XT I had was 5150 (the 2 full height floppy drive model) -- Antony T Curtis