That's the job of the BIOS extender.
bootstrap32 is a PM32 USB FAT32 bootloader which includes a free
BIOS extender (free in the sense that you are free to use it or
not once loaded). Over 5 years in development and production.
Tested on many PC's both old and new (with traditional BIOS).
Correctly handles System Management Mode transitions. Directly
supports the most commonly used BIOS functions. Access to the core
function which allows access to any native motherboard BIOS function.
No setup or special calls to make, just initialize the registers
and make an interrupt call.
http://mikegonta.com/bootstrap32.zip
Mike Gonta
look and see - many look but few see
http://mikegonta.com