Hi..
I'm looking for some documentation on an obscure PC data table!
I'm writing a program that replaces your MBR with new code. This new code 
allows lots of yummy features such as a "pre-boot" menu, allowing you to 
select with O.S. you wish to boot from, at boot time (no more running FDISK 
to change bootable OS's.. instead select from a menu at bootup), boot from 
drives other than the first floppy or hard disk, etc etc.
I've run into one problem. I need to know how to decode the LOGICAL drives in 
an Extended DOS partition. By decode I mean access the table stored on the 
HDD at head 0, cyl 0, sector 2, and recognise the logical partitions therein 
listed. I know that head 0 cyl 0 sect 2 is the place this table is stored, 
but I canonot seem to work out it's format, and no book I've got (and I have 
a lot of pretty good 'undocumented' books, swag, pcgpe, asnips, 80xxx snips, 
etc etc.) Every book covers the MBR, but then jumps straight into the dos 
boot sector, WITHOUT doccumenting the logical drives-in-an-extended-partition 
table!
Note: this code is MBR code. All you have is the BIOS at this point DOS does
not exist and cannot help. Suggestions involving DOS will be of no use!!
I will be making this program freely available and posting source (A86 
assembly) in this echo. Anyone who is interested in writing your own MBR 
program should reply to this message as I have also developed tools to 
read-modify-write new MBR's without trashing the Partition table, display 
menus from the MBR, use A86's code output directly etc etc.
I already have the code working, however It is still in an early form and can 
'only' boot partitions from the bios selected MBR at this point, however it 
CAN currently boot any primary partiton, active or not, via a menu and a user 
keypress.. something a lot better than the standard MBR! Please ask if you 
want to see the sourcecode.
It cann't boot from logical drives yet because I can't work out the damn 
table!! If I had the table's format, booting logical drives would then be 
just as easy!
I hope to develop a freeware equivilant to 'partition magic' eventually, once 
I get the necessary tools and basic documentation working.
Many thanks if you can help out!
       Craig
--- FMail/386 1.20+
---------------