OSDev.org

I am new at OS Programming, and do not know a whole lot about about x86 Assembly. I have been trying to access read data from a floppy drive using the following code (compiled with GCC):
asm(" movb $2, %ah
movb $4, %al
movb $0, %ch
movb $2, %cl
movb $0, %dh
movb $0, %dl
movw buffer, %bx
movw %bx, %es
mov $0, %bx
int $0x13
buffer: .long 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
");
It compiles correctly, but when I run it in the emulator Bochs, it exits and says:
Bochs is exiting with the following message:
[CPU  ] exception(): 3rd (13) exception with no resolution

I do not have any idea about diskio or anything like that. Thanks.

gcc creates 32 bit flat code. pmode for x86. your trying to call a real mode interrupt that does not exist in protected mode.

So if that can only be done in real mode, how do you read and write to disks in protected mode? Thanks.

With ports (PIO) or dma or real mode interrupt 0x13 inside of a vm86 task handler (which, essentially, emulates real mode in a protected environment (with a performance penalty, of course)).

Cheers,
Jeff

While it is possible to run it by switching from protected mode back to real mode, or in a virtual mode task, the best solution is to write your own disk drivers; the same applies to device drivers in general.

If you check the development links (especially the Operating Systems Resource Center), you should find tutorials on how low-level disk I/O works for both floppy and hard drives.