Public domain boot sector released_ compatible with MS-DOS 6.00 _ 6.22

Re: Public domain boot sector released, compatible with MS−DOS 6.00 & 6.22



Re: Public domain boot sector released,

compatible with MS−DOS 6.00 & 6.22



Source: http://coding.derkeiler.com/Archive/Assembler/alt.lang.asm/2011−07/msg00016.html







• From: "Rod Pemberton"

• Date: Sun, 3 Jul 2011 19:59:40 −0400



"Benjamin David Lunt" wrote in message

news:lX5Qp.49320$F25.7395@xxxxxxxxxxxxxxx





don't really know what $$ means





It's the "beginning of the current section" address, i.e., ORG in this case.

$ is the current address. E.g., $−$$ returns the offset from the start of

the section (ORG) to the current address.





Why do you use [bp + some_label_name − $$]

If ds = 0 and you used org 0x7C00, can't you just do

mov eax,[some_label_name]

I know that you have SS = 0 so you are using BP, but

isn't it smaller to set DS to 0, and use only the offset?







I suspect he developed with a different ORG value, i.e., 0, e.g., DOS .com,

but I'm not too sure why... If he was testing with data already at 7c00,

maybe...





One thing that I have always had a problem with is booting from one

volume, scanning for all other volumes across multiple disks, then

knowing which one of those found volumes was the volume we booted

from. For example, when we boot, we know that the BIOS gave us

a value of 0x81 in DL, but there are three volumes on that disk.

Which one of those three volumes did we boot?





Huh? Do you mean the "volume" that has the partition marked bootable?

Doesn't the value in DL correspond to the _device_ booted? And, the

_volume_ booted is base on the bootable flag in the partition table, yes?

How do you select another volume to boot without a boot manager? Without

user interaction, e.g., BIOS BBS pop−up boot selection window, the bootable



Re: Public domain boot sector released, compatible with MS−DOS 6.00 & 6.22 1

Re: Public domain boot sector released, compatible with MS−DOS 6.00 & 6.22

partition on the lowest ranked bootable device is going to be booted by

BIOS, yes?





Yes, we know that

we booted from LBA 10,000, but how do you connect the volume

at physical LBA 10,000 with DL = 0x81 and the volume you booted

from? Something to think about, huh?





I know you're very well versed in this, but I'm more than a bit confused by

your description of what happens... That's not what I understood to happen.

Could you explain?





Rod Pemberton







.









Re: Public domain boot sector released, compatible with MS−DOS 6.00 & 6.22 2