From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.33) id 1BliIT-0003av-C2 for qemu-devel@nongnu.org; Sat, 17 Jul 2004 02:03:45 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.33) id 1BliIR-0003a4-Ey for qemu-devel@nongnu.org; Sat, 17 Jul 2004 02:03:45 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.33) id 1BliIR-0003Zx-CQ for qemu-devel@nongnu.org; Sat, 17 Jul 2004 02:03:43 -0400 Received: from [80.59.103.181] (helo=claunia.com) by monty-python.gnu.org with esmtp (TLSv1:DES-CBC3-SHA:168) (Exim 4.34) id 1BliFN-0003qX-K4 for qemu-devel@nongnu.org; Sat, 17 Jul 2004 02:00:38 -0400 From: "Natalia Portillo" Date: Sat, 17 Jul 2004 07:01:27 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: Subject: [Qemu-devel] BIOS behaves different as real BIOS 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 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-). Regards, Natalia Portillo P.S.: Just have read the BIOS source code from the original IBM PC documentation, and BIOS doesn't look for that signature, just do INT 13h to copy the first sector from floppy 0 to 0x7c00 and then jump to it, just as following (is NOT a copy from the documentation): Mov ah, 02h Mov al, 01h Xor ch, ch Mov cl, 01h Xor dx, dx Mov ex, 0000h Mov bx, 7c00h Jmp 7c00h P.S.2: Maybe this mail should be better sent to bochs mailing list but I'm not subscrided, so, if so, please resend it.