question about bios process

[luck05]

when you turn on your computer,the bios does:



1- check the cmos for custom settings
2- the bios loads into the MEMORY the device driver and intreput handlers
3- intializes cpu registers.
4- performe the post(ram, monitor , keyboard,...)



the question is about step number 2: the bios loads into memory the device driver and interput handlers.



what's the memory talking about ?



because as i understand ,.it can not use the ram before post checking process , so what's the memory they talking about ?

 

[michalrz]

I think step 4 (POST) happens first. Then and there the bios code performs fundamental checks like available registers (there are also chipset registers!) and main memory check.
The CPU instruction set contains means to handle basic input/output, like writing to the screen, so no drivers are really necessary at this point.
When boot-time comes finally, control is handed over to the second stage bootloader, like NTLDR, which also can use rudementary, slow methods to begin loading the actual Windows drivers and system files into main memory. So, basically even without "real" drivers, the computer has hardcoded means to handle hardware.
And if I understand correctly, without RAM, the EPROM chip acts as 'memory' and the CPU can fetch and write to it.

Edit: as I was refreshing my info, I found this: Detecting Memory (x86) - OSDev Wiki I think it explains the issue way better than I did