Date: Thu, 20 Aug 1998 11:44:01 +0800 From: Fook Sheng <chen68@hotmail.com> To: "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG> Subject: boot sector - Please help!!!!!!!!!!!! Message-ID: <35DB9B7F.40599116@hotmail.com>
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Hi
I'm trying very hard to write a boot sector, and I have some doubts
which I really need your kind help. I intend to use Intel platform.
This is what I know :
When the system is reset or booted-up,
Loads Sector 1, Track 0, Head 0 of the boot drive( A or C ) to absolute
address 07C00h-07DFFh.
Checks the word at absolute address 07DFEh for AA55h. This is the boot
signature and is used by the BIOS to ensure that the sector contains a
valid bootsector. If this signature isn't present, the BIOS will display
an error message.
Loads DL with:
00h if the boot sector was loaded from floppy disk,
80h if the boot sector was loaded from hard disk.
This way, the bootsector knows which drive it was booted from.
Jumps to 0000:7C00h, which is the start of the bootsector
(my questions are :)
The boot sector then has to locate and load the kernel from the harddisk
using BIOS interrupt (am I correct?) and transfer control to the kernal
by using a JMP(am I right?)
is the source for freebsd's boot sector in /usr/src/sys/i386/boot? I can
find directories like netboot, rawboot, dosboot, biosboot and kzipboot,
can anyone tell me what each of these directories do? I guess for my
case I should look into biosboot since I'm using BIOS to load my kernel
(if I ever manage to write one!!), am I right?
I hope I'mnot asking for too much, and I apologize if that is the case.
I am trying to write a small little kernel just for interest, but my
knowledge is very limited so I really appreciate if anyone can help me
out by any means, if possible please give me any related links.
Thanks so much in advance.
Chan Fook Sheng
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