Hello, I'm in the middle of studying disk organisation to enhance my
understanding in this area. I have a few questions about fdisk (trying
to fill a gap in my knowledge if that's ok)...
In the below output of fdisk it shows (correctly) a geometry of 224
heads, 56 sectors/track. I'm unclear about where this information comes
from. Normally a disk's geometry would be reported as 255 heads and 63
sectors. I explicitly partitioned this disk using a 224/56 geometry, so
the report is correct. I'd just like to understand:
(a) where fdisk gets the information about the geometry from in this
specific case?
(b) when fdisk defaults to 255/63 is that because it's hard coded that
way or is there another reason?
I understand why it's 255/63 by default but haven't been able to
understand how the geometry is determined. I do know that it's all kind
of moot these days anyway because of sector based addressing but that
leads to one other question: given sector based addressing why does
fdisk even bother displaying a geometry any more ? Doesn't it just serve
to confuse?
# fdisk /dev/sda
Welcome to fdisk (util-linux 2.21.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p
Disk /dev/sda: 80.0 GB, 80026361856 bytes
224 heads, 56 sectors/track, 12460 cylinders, total 156301488 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc4c4122e
Device Boot Start End Blocks Id System
/dev/sda1 * 56 501759 250852 83 Linux
/dev/sda2 501760 156298239 77898240 8e Linux LVM
Command (m for help): q
Many thanks for your time,
John Lane.
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