BIOS versus direct access

Direct access (without BIOS):

• reading and writing data directly through the hard disk controller.

  • the software needs to know how to address the controller and how to issue commands to it.

  • it needs to know the commands code for: read, write, ...

  • it needs also how to query the hard disk for details such as type and size.

  • this method is more complex, but also faster.

  • modern OS perform direct accesses to disks.

Access with BIOS:

• slower than direct access.

• but simpler, the BIOS does all the work.

• the BIOS provides services to the software to communicate with the hardware.

  • INT 13h and extendedINT 13h

• nowadays it is only used in the boot process.