On Wed, 10 Mar 2010, Tejun Heo wrote:
Yes, the geometry is basically arbitrary values which can be queried
using a BIOS call and the reason why SCSI hosts can choose them is
they implement BIOS extensions themselves.
I mentioned SCSI host adapters to show that 64/32 geometry is no problem
for Linux (and other OS-es). Really is 255/63 hardcoded in many places?
If not, then geometry can be read from partition table.
From where?
From the ending CHS values of partition if it ends at cylinder boundary.
How do you calculate geometry from newer Windows partition tables (cases
W-1, W-2 and W-3)?
For modern OSes, geometry doesn't matter at all. Older ones are the
ones having problems (I've been corrected: XP seems okay while 2000
depends on CHS).
You are proposing "doing what Windows is doing". This way:
1. Partitions are aligned at 1 MiB (which is very good).
2. Geometry is "standard", i.e. 255/63 (which is good).
3. Partitions don't start and end at cylinder boundary (which is not so
good).
With 64/32 you can have:
1. Partitions aligned at 1 MiB.
2. Geometry is not standard, but is widely used (SCSI disks, USB flash
disks).
3. Partitions start and end at cylinder boundary.
--
Tomasz Palac, AGH University of Science and Technology
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