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Organization
of the data on the disks
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You now know, a Hard disk has cylinders, heads and
sectors. If you look in your BIOS you will find these
3 values listed for each Hard disk in your computer. You
learned that a Hard disk don’t have a fixed sector
size as they had in earlie r days.
Today, these values are only used for compatibility with
DOS, as they have nothing to do with the physical geometry
of the drive. The Hard disk calculates these values into
a logical block address (LBA) and then this LBA value
is converted into the real cylinder, head and sector values.
Modern BIOS’ are able to use LBA, so limitations
like the 504 MB barrier are now gone.
Cylinder, heads and sectors are still used in DOS environments.
SCSI drives have always used LBA to access data on the
Hard disk. Modern operating systems access data via LBA
directly without using the BIOS.
Transfer rates
In the pictures you can see the several ways how data
can be stored physically on the Hard disk. With a benchmark
program that calculates the transfer rate or seek time
of the whole Hard disk you can see if your drive is using
a 'vertical' or a 'horizontal' mapping. Depending on what
kind of read/write heads and servo-motors (for positioning
the actuator arm) are used it is faster to switch heads
or to change tracks. |
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