Reference
Track
A “track” is a concentric region for data
storage that is separated on a magnetic
disk.
●Construction of magnetic disks
In order to use a magnetic disk, it is first necessary to “format (initialize)”
the disk. The formatting organizes the disks into “tracks” and “sectors”
to enable the storage of data.
The construction of a magnetic disk is shown below.
Reference
Sector
A “sector” is a region of data storage
that is derived by radially dividing a
track into equal parts. It is the smallest
storage unit of a magnetic disk.
Track
Sector
Magnetic disks (floppy disks and
hard disks) store data in sector
units.
Moves in line with the magnetic head
(Seek operation)
Reference
Cylinder
A “cylinder” comprises a group of tracks
that share the same location. Each storage surface has its own magnetic head.
These heads move in line with each
other simultaneously, which makes it
possible to select tracks on the same
radius. The groups of tracks on the
same radius comprise a cylindrical
shape or cylinder.
Access arm
Magnetic head
Cylinder 2
Magnetic disk
Rotational axis
Cylinder 1
●Sequence for read/write operations of magnetic disks
Magnetic head moves to the target track. (Seek operation)
Reference
Search time
“Search time” refers to rotational latency
for read/write operations on a magnetic
disk. It is the time it takes after the seek
operation has finished, for the magnetic
disk to rotate, and for the lead part of
the read data or write area to reach the
position of the magnetic head. The seek
operation time is called “seek time.”
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Waits for the target sector to rotate and come around.
(Rotational latency)
Reads and writes to and from the target sector. (Data transfer)
●Fragmentation and optimization (defragmentation)
“Fragmentation” occurs when data is stored across multiple regions of
the hard disk. Repeatedly adding, deleting, and moving data that is stored
across a continuous sector results in a state of fragmentation. When data
becomes fragmented, the number of seek operations increases, which in
turn reduces access speed. It is then necessary to periodically repair fragmentation via “optimization,” which is performed using specialized software.