How does BIOS communicate with OS while booting?

[hariece]

I like to know the ways that BIOS can transfer information to the operating system while the system is booting up.

1.Can BIOS reserve some DRAM for its use during boot and place information in this area and inform Operating System that it has some information for use.
2. How can the BIOS notify OS that it has some information in the DRAM that has to be considered while OS boot up?
3. My computer has poweron password and OS password. I need to provide both the passwords if i had just powered up. But if i restart/reboot the OS (windows XP) it skips prompting for powerON password and directly asks for OS password. Is this because the machine was not totally coming up from power down or is it because the powerON password is stored in the DRAM by BIOS to use it when it is booting next time?

If this is wrong forum for this techincal question.... let me know the proper one.

Thanks in advance!!!!!!!
Hari.