grub error with dodgy cmos battery -- curiosity questiononly

[Bionut]

I have a curious phenomenon that I don't fully understand and was wondering if anyone could help me out.

Basically what happened is this;

Have a dodgy old lappy (IBM Thinkpad) and its CMOS battery was running low causing havoc. As this happened, grub would boot the kernel but this returned an unusual panic in the first few lines that I was not able to decipher.
I, after much frustration and bashing of heads against the wall, ascertained that if I re-installed grub, the kernel would do as it should and all was fine.

I guess the technicality is that somehow the low CMOS batt was causing some error in the BIOS drive allocation and as a result, **poooof*

So my question is more or less is there a more technical explanation for this phenomenon or am I around the mark and should shut up and not ask any more questions because I won't understand anyway? I guess this is out of curiosity and little else so only bother if you can be arsed... I just like to know what's going on under the hood as best I can

Ta

[NeddySeagoon]

Bionut,

The CMOS stores the disk drive geometry ans the access mode, e.g. C/H/S or LBA.
If this gets forgotten/corrupt by a low CMOS battery, the machiine cannot boot as it will read the secors off the disk in the wrong order.

However, this data is protected by a checksum. If the checksom test on power up fails, the PC should enter BIOS without any prompting. Save and exit will fix the checksum without correcting the corrupt data. The kernel gets the disk info from the disk itself, so once its running, the BIOS conted has no effect.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.