Hard Disk Boot ROM

NTDEV
1

Hi all,

Could some body share some information about the Boot ROM image on a bootable hard disk? Such as how does it communicate with system BIOS? Anything would be highly appreciated.

Alex

2

Like INT 21H real mode disk services or whatever is right for UEFI. There
used to be a boot bios test program in the WHQL tests. I assume a bunch of
other BIOS services are called too, like the 8200h memory layout (forget the
details), and perhaps calls to PCI and SM BIOS?

Also note that if you have a TPM, I believe the boot loader now will want to
measure the boot code integrity.

There is public code in gPXE that shows implementing the INT 21H disk
interfaces for iSCSI booting.

Jan

Could some body share some information about the Boot ROM image on a
bootable hard disk? Such as how does it communicate with system BIOS?
Anything would be highly appreciated.

3

Jan Bottorff wrote:

Like INT 21H real mode disk services or whatever is right for UEFI.

Well, INT 21H is provided by MS-DOS, which is not yet present at the
time the boot ROM runs. The boot ROM is going to use INT 13H to access
the disk BIOS, I believe.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

4

Oops, your right Tim, I meant to say 13H not 21H, what was I thinking,
thanks for the correction. I tried to forget all about BIOS API’s many years
ago, but a few years ago found myself debugging boot bios code.

Jan

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:bounce-420885-
xxxxx@lists.osr.com] On Behalf Of Tim Roberts
Sent: Tuesday, August 10, 2010 5:35 PM
To: Windows System Software Devs Interest List
Subject: Re: [ntdev] Hard Disk Boot ROM

Jan Bottorff wrote:
> Like INT 21H real mode disk services or whatever is right for UEFI.

Well, INT 21H is provided by MS-DOS, which is not yet present at the time
the
boot ROM runs. The boot ROM is going to use INT 13H to access the disk
BIOS, I believe.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

NTDEV is sponsored by OSR

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5

Also, you require more than a TPM in order to have to worry about
attestation and measurement.

mm

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Jan Bottorff
Sent: Tuesday, August 10, 2010 8:49 PM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] Hard Disk Boot ROM

Oops, your right Tim, I meant to say 13H not 21H, what was I thinking,
thanks for the correction. I tried to forget all about BIOS API’s many years
ago, but a few years ago found myself debugging boot bios code.

Jan

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:bounce-420885-
xxxxx@lists.osr.com] On Behalf Of Tim Roberts
Sent: Tuesday, August 10, 2010 5:35 PM
To: Windows System Software Devs Interest List
Subject: Re: [ntdev] Hard Disk Boot ROM

Jan Bottorff wrote:
> Like INT 21H real mode disk services or whatever is right for UEFI.

Well, INT 21H is provided by MS-DOS, which is not yet present at the
time
the
boot ROM runs. The boot ROM is going to use INT 13H to access the
disk BIOS, I believe.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

NTDEV is sponsored by OSR

For our schedule of WDF, WDM, debugging and other seminars visit:
http://www.osr.com/seminars

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

NTDEV is sponsored by OSR

For our schedule of WDF, WDM, debugging and other seminars visit:
http://www.osr.com/seminars

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

6

Thanks a lot to you all.
Is it correct that there are separate boot ROM images to support Legacy BIOS and UEFI? Is there any links you guys have in terms of how to implement the images?

Alex

7

(I’m having trouble with your term “boot ROM images”… and “boot ROM images on a bootable
hard disk” in your initial post… I’m not sure what this is referring to, precisely. If you could clarify in a follow-up that’d be helpful. In the meantime, I’ll answer based on what I *assume* you mean.)

Well… booting via Legacy BIOS and booting via UEFI are definitely different processes, if that’s what you’re asking. The boot ROM *in the machine* is different, and partition table format is different. UEFI is like it’s own pre-boot operating system, with video and storage services and the like.

There’s a very nice presentation by Murali Ravirala (MSFT kernel group) about Windows boot process: http://www.uefi.org/events/UEFI-Plugfest-WindowsBootEnvironment.pdf – that’ll give you SOME info anyhow.

Peter
OSR

8

Thanks a lot, Peter.
What I meant about the “Boot ROM images” was the binary codes save in the option ROM on a let’s say SCSI controller. The image talks to BIOS while POST to be identified as an IPL.

Alex

9

> What I meant about the “Boot ROM images” was the binary codes save in the option ROM

And how can it be put on the harddisk? it is in the ROM chip on the controller, not on the hard disk.

–
Maxim S. Shatskih
Windows DDK MVP
xxxxx@storagecraft.com
http://www.storagecraft.com