Total BIOS size > 64K - how it is accessed?

[vic]

Hello,
In the spec for my notebook I've found that flash memory may contain up to 1MB, so this means that theoretically bios can occupy up to this length. In reality downloaded image of the bios occupies about 300K. So my question is: Is that true that whole bios resides (mapped) in first 1M of memory ? If not, which machanisms (overlaying,remapping,windowing?) are used to make whole bios code/data accessible when needed ? Also is it true that ussually bios is executed in real mode when machine is powered ?

Reply or reference is highly appreciated,
Vic.

[Ghost_Hacker]

Also is it true that ussually bios is executed in real mode when machine is powered ?

Yes, all BIOS functions take place in real mode because only real mode memory addressing is "on" when you first turn on your computer.


Is that true that whole bios resides (mapped) in first 1M of memory ? If not, which machanisms (overlaying,remapping,windowing?)...

Yes, the BIOS does reside in the first 1M of memory.(Again because of the "real mode" memory addressing limitation) BIOS Shadowing is used to copy BIOS code from ROM to the upper memory (Above 640k, below 1M) range of RAM memory but this is an optional setting.



[This message has been edited by Ghost_Hacker (edited 02-06-2002).]

[Ghost_Hacker]

Hmmm my first answer is misleading....

Yes, all BIOS functions take place in real mode because only real mode memory addressing is "on" when you first turn on your computer.


BIOS functions are always in real mode. What I should have said is that only BIOS functions can work when the computer is first booted up because only real mode addressing is "on" at that time.


Hope I didn't confuse you http://www.PCGuide.com/ubb/smile.gif

[vic]

Thanks very much for the answer. Actually what I'm trying to figure out is how my BIOS image is layed out in the memory and how it is being accessed during machine bootup procedure. This whole interest is triggered by my PCMCIA controller which does not seem to function correctly on my model, while it behaves OK on similiar.
Does anyone know any references where implemented approaches to "BIOS Shadowing" are explained ?

[Ghost_Hacker]

Try these links some of them might help you:
http://www.geocities.com/SiliconValley/1212/mreal.html
http://www.osdata.com/system/physical/memmap.htm
http://www.pcguide.com/ref/mbsys/bios/bootSequence-c.html
http://www.eonlinetraining.com/APlusWin/section2/topic3.htm
http://www.cs.umbc.edu/courses/undergraduate/CMSC211/Spring01/burt/ administrivia/BIOSandDOS_Interrupts.html (http://www.cs.umbc.edu/courses/undergraduate/CMSC211/Spring01/burt/administrivia/BIOSandDOS_Interrupts.html)


Good luck http://www.PCGuide.com/ubb/smile.gif




[This message has been edited by Ghost_Hacker (edited 02-07-2002).]

[rond36]

vic, You may want to read my post in this thread (http://www.pcguide.com/ubb/Forum8/HTML/000629.html) it could explain the size difference between the flash file and the BIOS.

------------------
I think Windows XP and Microsoft use more of my bandwidth than I do!
WindowsBBS.com (http://www.WindowsBBS.com/index.php?referrerid=115) Is back online, check it out