How is BIOS addressed (accessed) after the O.S is loaded?

[theKbStockpiler]

Lets say a BIOS interrupt is requested after the O.S is loaded. How is the BIOS code made available? Is it left it RAM even after the O.S boots?

[Rubberman]

It depends. Some BIOS's are real-mode only, accessible via INT 10. Some have protected mode capabilities (most current systems). I'm not sure which interrupt will access the protected mode BIOS since it has been about 20 years since I last had to deal with that cruft...

As for your last question - no, it is not "left in ram". It is in ROM, but addressable and accessible by any priviledged program that can map the correct physical addresses where the BIOS resides.

[theKbStockpiler]

So basically BIOS is always connected to a bus and not read from a reserved memory location?


I was short on time during the " How to Unlock Yum but am going to get back to It.


Thanks again!

[Rubberman]

So basically BIOS is always connected to a bus and not read from a reserved memory location?


I was short on time during the " How to Unlock Yum but am going to get back to It.


Thanks again!

It is in a reserved location, but that is mapped physical memory in ROM/Flash, not RAM. IE, it can be read/executed, but not written to without special software to update it. A long time ago, it was real ROM memory, then EEPROM (Electrically Erasable Programmable Read-Only Memory), now flash ROM, which is similar to EEPROM's, but uses different memory technology. So, consider the BIOS to be Read-Only Memory (ROM) vs. system random access memory (RAM). Are we confused yet?