[Gllug] Partioning advice needed

[Mike Brodbelt]

Pete Ryland wrote:
> On 15/02/07, Dan Kolb <gllug at eco.li> wrote:
>> I can't comment about sd2, but you do need sda3. As a relic of the good ol'
>> days of DOS, you can have up to four primary partitions, everything else would
>> have to live in an extended partition. DOS' fdisk would only allow you to
>> create one primary and one extended partition, which would be split into
>> various logical drives.
> 
> Actually, this is one that we can't blame MS for.  It's the BIOS that
> traditionally uses the partition table, and they only provided room
> for four entries.

No it isn't - the BIOS carries out the POST and hardware initialisation,
then it loads sector 0, track 0 of the first fixed disk (or floppy, or
thing that emulates a floppy) at 0x7c00 IIRR, and passes control to it.
The BIOS has no knowledge of partition tables whatsoever. That sector
must contain a program that is capable of starting the bootstrap
process, but that's all. The bootsector structures, and (in the case of
a fixed partitionable disk) the partition table structure, were defined
by MS-DOS. The bootsector came first, as early DOS releases didn't
support hard disks, and initially didn't support partitioning them.

> The "extended partition" is treated as another disk, and holds a
> partition table of its own, capable of holding four entries too, but
> usually the disks are set up as a chain of extended partitions, even
> though this isn't exposed as such, wasting a (logical) cylinder per
> partition!

Yes, this was another in a long chain of hacks necessitated by hard
disks growing faster than people thought they would. A 12-bit FAT
doesn't go that far before your cluster size starts getting really wasteful.

Mike
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