Re: more ram and larger harddrive then the bios can take

["Jens B. Jorgensen" <jjorgens@bdsinc.com>]

Jeff,

I recently had the displeasure of finding out all about limits with disk size. I
purchased a 10.1GB IDE disk. Here's the lowdown, gleaned from the in-depth BIOS FAQ at
ftp://ftp.wi.leidenuniv.nl:/pub/faqs/bios.faq. boot sectors use the BIOS Int 13H
service to read blocks from disks. This call takes a C/H/S address and reads a block
for you. This interface allows you to specify at most 256 heads, 1024 cylinders and 63
sectors. Multiply those three numbers * 512 bytes and you'll end up with 8GB. The
physical ATA interface allows you to address disks with up to 16 heads, 65535
cylinders, and 63 sectors. ATA devices also allow LBA addressing which simply takes a
block number and lets you address 2^28 sectors (137GB). Now, if you look at the limits
for the BIOS interface and the physical interface you'll soon see that all kinds of
ugly mapping and nastiness get involved.

I was never able to get my PC (a 3 year old pentium) to access more than 8.4GB. Even
that was only after flashing my ROM to the latest version. I could access the entire
drive from both Win98 and Linux if the drive was a secondary (non-boot) drive.
However, I needed to remove the other drives from the system so I was stuck. My advice
is to read the above FAQ and proceed with caution.

Jeff Katcher wrote:

> Per-Olof Widstrom wrote:
> >
> >  I have seen that people get the advise to add a line in lilo.conf that
> > tells how much RAM the system have, if they have more then 64 mb, and that
> > it is possible to have a larger harddirve then the BIOS can handle. I just
> > would like to ask two simple questons about this:
> >
> > Q1
> >   I have a motherboard with a bios that take 128 ram, no more, that is
> > what the manual says, can I have 256 mb if I add memory=256 in lilo.conf.
>
> A1
>   No
>
> >
> > Q2
> >   My bios manual say that it´s limit is 8,4 gb harddrive. But if i have
> > the root inside the 8,4 gb limit is it possible to have, lets say, a 15 gb
> > hardrive?
>
> A2
>   No
>
> Disclaimer:
>         I am guessing at these, so take what I say with a Grain of salt.
>
> I would say that both of these are Hardware Limitations, not software or
> driver limitations.  Physical as opposed to Logical problems and thus
> not correctable by software.
>
> Jeff
>
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--
Jens B. Jorgensen
jjorgens@bdsinc.com