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Hard Disk Drive

The hard drive is considered as the secondary memory in the computer. The hard drive is used to backup data as well store the information in the computer as the secondary device. In contrast to RAM hard drive is the secondary memory that can retain the data even if there is a power failure. The RAM that is a primary memory will lose the data when ever there is a power failure. Although there are some sort of RAM available that are non volatile and can store up the data even if there is a power failure.

It is usually a magnetic disk that holds the data permanently. They are usually faster and can access the data much faster than the floppy drive as well. The hard disks usually come in two types that is in ATA/IDE or SCSI. The hard drive usually has the platters in it. The hard drive was first made by the IBM in the year of 1956 that was the RAMAC that had its platters as two feet in diameter. Later on the size reduced physically and the size in terms of memory increased.

The access speed varies from drive to drive; in fact the hard drives with higher access speed are much costlier than those that have less access speed in terms of rpm. Even as the memory increases the cost also correspondingly increases. The hard drives are usually of two types one is internal hard drive also called as the non removable hard disk.

The above mentioned type of hard drive is internally fixed in the computer system. The other type of hard drive is that which is external and have a hard casing over it. The second type of hard drive is usually portable and has USB connectivity. The hard drive which is today in the present form was first made by Seagate in 1979. It had the memory size of about 5MB. But in comparison to RAMAC which was the first ever hard drive made by IBM it had 10 times more storage capacity.

The hard drive consists of platters which has the magnetic surface over which the data could be stored. Anyway listed below are some of the important factors that may help in the determination of the performance of the hard drive.

Rotational latency:

It is defined as the time that elapses when the read/write head is over a position to the time the first byte of the data is on the head.

Seek Time:

It is defined as the time with which the disk can position its head over any data. Since data may reside even some where else hence this time may be more or less. So an Average Seek Time is considered.

Internal Data Rate:

It is defined as the speed with which the disks internal read head can transfer data from the magnetic media.

Access Time:

It is defined as latency plus seek time.

Apart from all these factors there others like external data rate, command over head etc.

The most popular manufacturers of the hard drives are Seagate, Western Digital, Quantum, Samsung, Atari etc.

Today hard drives are available in many capacities like from 20GB up to in terms of Tera Bytes as well.

Changing the trend IBM has launched a new type of storage device called as the millipede. This is much smaller in size and uses the technological concept of MEMS - Micro-electrical-mechanical system. Future storage devices may replace the current types of hard drives.

The laptop hard drives are much smaller in physical size. Apart from the hard drives the other storage medium may include the optical disk, flash memory disk, magnetic tape, magnetic disk and other new form of storage devices that are still under research and development.

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