Re: offset 63 or 0 for disklabel/fdisk?

[Nick Holland <nick@holland-consulting.net>]

Sven Kirmess wrote:
> 
> I guess that's a FAQ and I am sorry about asking this but I could not
> find the answer.
> 
> When I give the whole disk to OpenBSD during the installation it
> creates a partition like this:
> 
> *3: A6    0   1   1 -  262 254  63 [        63 -    4225032] OpenBSD
> 
> Why does it not create a partition like starting at head 0 or why does
> it leave the first 64 (0 - 63) blocks free? Are they all used for the
> MBR?
> 
> In the manpage of fdisk (3.0) we have an example like this:
> 
> *0: A6    0   0   1 -   79   1  18 [         0 -       2880] OpenBSD
> 
> Is this valid (starting at head 0)?
> 
> Sven

Depends upon the platform.

i386 likes a one head offset...  It isn't 63 sectors, but one entire
"track" (which on virtually all modern drives *is* 63, but stick an
old 200M IDE in, or use an MFM drive and this number will vary) (also
keep in mind on a PC with IDE drives, those numbers are all bogus
anyway).  The boot record and partition table only take up one sector,
however some partition managers load themself in that area, and
general convention is to leave it free, and considering the small
amount of space we are talking, be safe, follow convention. 8-)

Sparc doesn't need that offset -- totally pointless and even incorrect
to use it.

Mac68k: not applicable. (actually, that's not really true, but things
are "different" on a Mac...and it isn't 63 sectors).

hmmm...those are the platforms I know.  I suspect most of the non-PC
platforms will start from zero.

Nick.
-- 
http://www.holland-consulting.net