On Wed, 2008-06-04 at 23:12 +0000, A Darren Dunham wrote:
> Best story I've heard is that it dates from before the time when
> modifiable (or at least *easily* modifiable) slices didn't exist. No
> hopping into 'format' or using 'fmthard'. Instead, your disk came with
> an entry in 'format.dat' with several fixed slices.
format.dat? bah. in some systems I used - notably 4.2/4.3BSD on the
vax and some even more obscure hardware - the partition table was
*compiled into the device driver* (one table per known disk type).
Don't like the partition layout? you have kernel source, you can change
it...
Disk labels didn't turn up until after BSD4.3.
> So you could use the entire disk with any of:
> a,b,d,e,f,g
> a,b,d,e,h
> c
Right. You'd typically use the a/b/d/e/f/g or a/b/d/e/h slice on your
boot disk and the c slice on additional disks.
> without having to change the label.
And the reason why changing the label was avoided was because it
required recompiling the kernel and rebooting.
> I speculate that then utilities were written that used c/2 for
> information about the entire disk and people thought keeping the
> convention going was good.
it's more like it was too painful to change.
> You can later use access to block 0 (via any slice) to corrupt (...er
> *modify*) that label, but that's not a feature of s2. s0 would do it as
> well with the way most disks are labled (because it also contains
> cylinder 0/block 0.)
and why didn't this get fixed? inertia. because slices are implemented
in the disk driver by looking at the low order bits of the disk minor
number, you couldn't just wedge in an additional device instance for the
unsliced disk without taking away one slice or re-creating *all* of your
disk block & character devices.
- Bill
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