Main technical specification and parameter of hard disk

Main technical specification and parameter of hard disk
Capacity
We can see the capacity in two aspects: the total capacity and the capacity of one disk. The whole
capacity is made up of each disk capacity.
If we increase the disk capacity, we would not only improve the disk capacity, improve the speed
of transmission, but also cut the cost down.
Rotate speed.
Rotate speed is the speed disk rotate. It is measured by RPM (Round Per Minute).The rotate speed
of IDE hard disk are 5400RPM, 7200RPM etc.
Average Seek Time
The average seek time gives a good measure of the speed of the drive in a multi-user environment
where successive read/write request are largely uncorrelated.
Ten ms is common for a hard disk and 200 ms for an eight-speed CD-ROM.
Average Latency
The hard disk platters are spinning around at high speed, and the spin speed is not synchronized to
the process that moves the read/write heads to the correct cylinder on a random access on the hard
disk. Therefore, at the time that the heads arrive at the correct cylinder, the actual sector that is
needed may be anywhere. After the actuator assembly has completed its seek to the correct track,
the drive must wait for the correct sector to come around to where the read/write heads are located.
This time is called . Latency is directly related to the spindle speed of the drive and such is
influenced solely by the drive's spindle characteristics. This operation page discussing spindle
speeds also contains information relevant to latency.
Conceptually, latency is rather simple to understand; it is also easy to calculate. The faster the disk
is spinning, the quicker the correct sector will rotate under the heads, and the lower latency will be.
Sometimes the sector will be at just the right spot when the seek is completed, and the latency for
that access will be close to zero. Sometimes the needed sector will have just passed the head and
in this "worst case", a full rotation will be needed before the sector can be read. On average,
latency will be half the time it takes for a full rotation of the disk.