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Index > OS Construction > All-in-one vs. one-for-each bootstrap loader

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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
The questions:

1. Is boot loader an integral part of file system, or it should be versatile?

For example, should 90mm FD boot loader consider FAT16/FAT32/whatever as a possible FS?

2. Even more, should boot loader written to 80/2/18 90mm FD adopt another geometry?

3. And to "finish him!", could boot loader for FAT12 formatted 80/2/18 90mm FD be hard-coded to ignore BPB and go on it's own calculations?

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Post 15 Jan 2009, 22:05
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mikegonta



Joined: 20 Nov 2005
Posts: 99
mikegonta
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Last edited by mikegonta on 28 Jan 2009, 09:04; edited 1 time in total
Post 17 Jan 2009, 00:26
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
mikegonta,

BIOSes already use FAT12 FS, for flash functions (so BPB is used by BIOS Wink).

If boot loader is a BIOS concept, why Windows checks for 55 AA @ 1FE and EB xx 90/E9 xx xx @ 0?

OK, enough rant.

That's what I meant: bootstrap loader is a part of file system, thus it can be hard-coded to boot specifically using corresponding disk geometry and file system. I don't see much sense to copy bootstrap loader between different disks (with different geometry and/or file system).

Another big question is: will BIOS boot from 1024/2048/…/16k bytes-per-sector floppy? I'll check it later. Wink

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Post 17 Jan 2009, 21:15
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mikegonta



Joined: 20 Nov 2005
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mikegonta
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Last edited by mikegonta on 28 Jan 2009, 09:04; edited 1 time in total
Post 17 Jan 2009, 22:11
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neville



Joined: 13 Jul 2008
Posts: 507
Location: New Zealand
neville
The answers:

1. No, the bootloader has nothing to do with any filesystem. Yes, it should be versatile e.g. loading FAMOS Wink

2. It can. For example, booting a CD using floppy emulation. The BIOS thinks its a FD with a storage capacity of 18 MiB (18,874,368 bytes). The usual gemoetry assumed is CHS=256/2/18 with 2048-byte sectors.

3. Yes. As mikegonta has said, the BPB is pretty much ignored by the BIOS.

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Post 17 Jan 2009, 23:00
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