[syslinux] Getting classic BIOS and UEFI boot on the same disk?

Gregory Bartholomew gregory.lee.bartholomew at gmail.com
Sat Aug 31 11:14:37 PDT 2019

I don't think the classic BIOS systems read the partition table at all.
Rather, they just load the first 440 bytes from the drive into memory and
copy the memory address that it was loaded to a CPU register. From there,
it is up to that 440 byte program to decipher the partition table. If you
use syslinux's gptmbr.bin, you should be fine.

On Sat, Aug 31, 2019 at 4:47 AM Erik Rull <erik.rull at rdsoftware.de> wrote:

> Gregory Bartholomew wrote:
> > That is correct. "bls1 include" would cause errors without the patch.
> The main
> > parts of the script that would be relevant to you would be the parts
> that create
> > the partition, set its type codes, write the first-stage boot loader to
> the
> > first 440 bytes of the disk, and lay out the file system (e.g. it
> demonstrates
> > that a single /syslinux.cfg file can be shared between both the UEFI and
> > binaries). Much of the rest of it would be irrelevant for your case.
> Sounds good. What I did not find - maybe I'm not too deep in this topic -
> will
> the classic BIOS boot find a proper classic partition table? Or will it
> find
> only the GPT? The oldest system we have in operation has a AMI BIOS dated
> 2004 -
> will it be able to handle the GPT or do I need further modifications?
> (I'll have the answer at last next week after trying it out :-))
> Best regards,
> Erik

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