cheap computers hard drive

hard drives are important parts in a computer.

How hard drive works

A hard drice is made up not of only one disk, but several disks made of metal, glass or ceramics piled up one on top the others at a very short distance from each other. They turn very quickly around an axis ( several thousands of turns per minute) in the reverse direction of a watch.

A computer functions in a binary way, i.e. the data are stored in the form of 0 and 1 (called bits). On cheap computers hard drive There are million of these bits, stored very close from each other on a fine magnetic layer of a few microns thickness.

Reading and writing

On cheap computers hard drive reading and writing are done thanks to the read heads located on both sides of each platters) i.e. one of the disk composing the hard drive. These heads are electromagnets, which allow to read information or to write it.

These heads can laterally sweep the surface of the disk to to reach all surfaces... However, the heads are dependent between them and only one head can read or write at a given time. One thus speaks about cylinder to indicate the data stored vertically on the disks.

SCSI Interface

SCSI interface is an interface which can be adapted to a significant number of units (cheap computers hard drive, Cd-rom, burners, scanners...). It is used more for its stability in particular on the level of the rate of transfer. Indeed, in SCSI hard drive it is an SCSI adapter which takes care of the management and the transfer of the data with a dedicated processor. The central processor or CPU is then relegated of its activities concerning the data flow. It does not communicate with the SCSI adapter.

Thus each SCSI adapter or controller has his own characteristics (frequency...), the BIOS does not have any influence on the performances of SCSI interface since it has itself its own BIOS.

Characteristics of cheap computers hard drive

The rate of transfer is the quantity of data which can be read or written on the hard drive in a given time. It is expressed today in Megabytes per second.

The latency time represents the time passed between the moment when the hard drive finds the track and the moment when it finds the data.

The access time is time that the head takes to go from a track to the following track (it must be smallest possible).

The average access time is time that the hard drive takes between the moment when it received the order to provide data and the moment when it really provides them.

The radial density is the number of tracks per inch (TPI: Track per Inch).

The linear density is the number of bits per inch on a given track (BPI: Bit per Inch).

The surface density is the ratio of the linear density on the radial density (expresses itself out of square bit per inche).