Re: Large disks on old computer

From: Clive Dove (chdove_at_rogers.com)
Date: 09/16/04 

Date: Thu, 16 Sep 2004 13:33:18 GMT

dr wrote:

> "Jukka Aho" <jukka.aho@iki.fi> wrote in message
> news:<D1Q1d.1014$Kq1.492@reader1.news.jippii.net>...
>> Rick Moen wrote:
>>
>> > Don't forget about LBA48 addressing. If the BIOS is older than
>> > that,
>> > there's a 137GB limit. E.g., the good ol' Intel L440GX+
>> > "Lancewood" has that problem (unless, like me, you're using SCSI).
>>
>> I have a 80 GB and a 160 GB HDD attached to an i440LX motherboard,
>> which has the infamous Award BIOS version that crashes on drives
>> which report their capacity larger than 32 GB.
>>
>> The 80 GB HDD is a boot drive, and it has been adjusted (with an
>> MS-DOS tool provided by the manufacturer on their support pages)
>> to report its size as "32 GB" to the BIOS, so I can boot from it.
>> However, I have installed Dynamic Disk Overlay into the boot sector
>> (again, using an MS-DOS HDD prep tool provided by the HDD
>> manufacturer on their support pages). It takes over the BIOS software
>> interrupts and allows the system to see the whole capacity of the
>> drive, so I can e.g. boot to MS-DOS and see the whole drive.
>>
>> The other drive (160 GB) has not currently been set up to be visible
>> to the BIOS at all: the drive configuration has been manually set to
>> "None".
>>
>> As for Linux and Windows (W2K, XP) the BIOS restrictions (or setting
>> the drive detection in BIOS setup menus to "none" for secondary
>> drivess) does not really matter: once you have booted into 32-bit
>> mode, you are usually not using the BIOS calls for detecting or
>> handling the drives any loger.
>>
>> So, in effect, W2K and Linux see both drives just fine (and at
>> their full capacity!), even though the boot drive lies its size
>> to the BIOS (to get past the 32 GB limitation) and the information
>> about the existence of the other one has not even been entered
>> into the BIOS setup menu!
>
>
> I interpret this as: 'on any old PC I will be able to boot into Linux,
> from some appropriate device, and from Linux be able to fully access
> large* ([S]ATA) disks attached to a controller card -- assuming there
> exists a device driver for the card'. Any objections?
>
> large*: ~200GB
>
> Thank you for all answers! /dr

What you need to do to get linux to boot with an old bios is to have the
partition holding the /boot part of the tree entirely within the first
1024 cylinders. If your / partition would be too big, the customary
answer was to set up a small partition at the beginning of the drive
and mount it as /boot.

Then when you install linux, the /boot tree will be installed in that
partition and the rest of the root tree will go into a subsequent
partition mounted as / or into subsequent partitions mounted, for
example as / and /home etc. The /boot partition has to be big enough
to hold the entire /boot directory and small enough that it entirely
fits below cylinder 1023/ which is not a problem as the /boot directory
is a small one.

Once the bios has found the /boot partition and loaded the linux kernel,
linux will take over and find the rest of the drive without regard to
bios limitations. No special additional drive controllers are needed.

This technique was trite before LBA was intoduced. It was almost
automatic to simply start the drive architecture with a small /boot
partition.

Clive

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