hard disk in real mode

Hello everyone.

Programming in real mode, how can I determinate how many harddisks are
present in my pc ? and how they are numbered ?

And to use these function (and other):
Int 13/AH=03h - DISK - WRITE DISK SECTOR(S)
Int 13/AH=02h - DISK - READ SECTOR(S) INTO MEMORY

how can i know what is the maximum number of cylinder, head and sector per
each hardDisk ?
and what exactly does this mean ?
"DL = drive number (bit 7 set for hard disk)"
I have to set DL to my driver number and OR it with 0x40 ?

Thanks in advance
Cya
Matic

On Wed, 31 Mar 2004 21:47:00 +0000 (UTC), Matic <matic999@hotmail.com>
wrote:

>Hello everyone.
>
>Programming in real mode, how can I determinate how many harddisks are
>present in my pc ? and how they are numbered ?
>
>And to use these function (and other):
>Int 13/AH=03h - DISK - WRITE DISK SECTOR(S)
>Int 13/AH=02h - DISK - READ SECTOR(S) INTO MEMORY
>
>how can i know what is the maximum number of cylinder, head and sector per
>each hardDisk ?

>and what exactly does this mean ?
>"DL = drive number (bit 7 set for hard disk)"
>I have to set DL to my driver number and OR it with 0x40 ?
>
>Thanks in advance
>Cya
>Matic
>

You will find a lot of info in Ralf Brown's Interrupt List.

Note that if you expect to run on anything over 4 GB
you should probably forget about the CHS system
and go to LBA (Logical Block Addressing).

As for the DOS drive numbering, bit 7 is 80h, so the
first (0th) hard drive is 80h, which is almost always
called drive C, 81h would be D, and so on.

Hope this helps!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

Matic <matic999@hotmail.com> wrote:

>Programming in real mode, how can I determinate how many harddisks are
>present in my pc ?

The byte at linear address 0x475 contains the number of hard drives
known to the BIOS. In Turbo C:
unsigned num_hds = pb(0x40, 0x75);

>and how they are numbered ?

I don't think there's a standard for this; it depends on the OS,
how the hard drives are partitioned, and (for DOS and Windows)
the filesystem type for each partition.

>And to use these function (and other):
>Int 13/AH=03h - DISK - WRITE DISK SECTOR(S)
>Int 13/AH=02h - DISK - READ SECTOR(S) INTO MEMORY

These are fairly simple; see Ralf Brown's famous Interrupt List
(search for it).

>how can i know what is the maximum number of cylinder, head and sector per
>each hardDisk ?

Use INT 13h AH=08h to retrieve the hard disk geometry information.
Large (new!) hard drives may not have a valid CHS geometry,
so you should also look at using the LBA disk functions in the
BIOS: INT 13h AH=41h/AH=42h/AH=43h

>and what exactly does this mean ?
>"DL = drive number (bit 7 set for hard disk)"
>I have to set DL to my driver number and OR it with 0x40 ?

0x80 is the INT 13h number of the first hard drive,
0x81 is the second hard drive, etc.