Re: [gentoo-user] Boot partitions (WAS: migrating disks (from mounts to disklabels

[Mick]

On Tuesday 23 November 2010 17:18:56 David W Noon wrote:
> On Tue, 23 Nov 2010 17:20:02 +0100, Peter Humphrey wrote about Re:
> [gentoo-user] Boot partitions (WAS: migrating disks (from mounts to
>
> disklabels:
> >On Sunday 21 November 2010 16:22:15 David W Noon wrote:
> >> What I suspect is in the remainder of that space is a hidden primary
> >> partition containing a "transparent" bootstrap that augments the BIOS
> >> and permits booting from a logical/extended partition.  This would be
> >> similar to the old OS/2 Boot Manager, although that was hardly
> >> transparent.  This hidden partition was probably placed there by
> >> cfdisk when you first partitioned the drive and started it with an
> >> extended partition. The OS/2 FDISK.COM did something similar when
> >> the first partition on a drive was not a primary (including Boot
> >> Manager).
> >>
> >> A forensic examination of that area would be of interest.
> >
> >Including attempting creation of three more primary partitions. If
> >your hunch is right, the last will not be created as the allowable
> >four exist already.
>
> No, only 1 primary and Neil's extended partition would currently
> exist.  So it should be possible to create 2 more primaries, if there
> were space on the disk.
>
> >I don't believe your hunch is right though - it's just too complex to
> >be worthwhile for any but a very few customers.
>
> Not at all complex.  OS/2 has had the option to work that way since
> about 1987 on 80286 hardware (and written by Microsoft).
>
> >Nobody's answered my parenthetical question though: why do SCSI and
> >IDE interfaces allow different total numbers of partitions?
>
> They don't.
>
> The number of primary/extended partitions is limited to 4, and the
> number of logical drives is limited by the size of the extended
> partition.  If you can fit more partitions onto one drive than another,
> it is because either the drive is bigger or the partitions are smaller.

Errm, not exactly.  SCSI/SATAs are limited to 15 (inc. one extended partition) 
and old (legacy driven) IDEs are limited to some 63 partitions if I recall 
correctly.  If you use the new libata I think you only get 15 partitions for 
SATA/PATA.

I know, because I remember some years ago getting a bit over-enthusiastic with 
a new SATA drive and fdisk only to end up with partitions that I couldn't 
mount ...  O_o
-- 
Regards,
Mick