What is a hard disk? What are its features

Hard disk is one of the storage devices, developed to store huge amount of data. The introduction of high capacity hard disks for micro computer system solved two serious problems related to the limited storage capacity of diskettes.
First, as a business begins to use micro computers extensively, the amount of software acquired and data collected tends to grow substantially. As a result the number of diskettes required, increases, dramatically second, the largest file that can be accessed at one time is limited to the capacity of the main memory and the storage medium. A hard disk can store huge amount of data in a most convenient way.
In hard disk system, data is stored in the same way as it is on diskettes. A series of tracks are divided in to sectors when the disk is formatted. Hard disk is made out of a rigid substance that is capable of storing a greater amount of data than the soft material used for diskettes. The hard disk drives for the micro computer can be internal or external.
Hard Disk
In a disk pack, the access mechanism can position itself to access data from each of the 200 cylinder is a set of all tracks with the same distance from the axis about which the disk pack rotates. In this example there are 10 tracks in each cylinder.
The capacity of diskettes in wide use today ranges from 360KB to 144MB each. Microsoft hard disk capacity ranges from 10MB to 1GB or higher. Hard disks larger capacity allows the user to store larger files and larger programs than can be used with diskettes. Access time with the hard disk is much lower than that of diskette i.e., data retrieval is much faster with the hard disk than a diskette.

Characteristics of a Hard disk:

  1. They are rigid metal platters connected to a central spindle.
  2. The entire disk unit is placed in a permanently sealed container.
  3. Air that flow through the container is filtered to prevent contamination.
  4. The disks are rotated at a very high speed (usually around 3600 RPM)
  5. These disk drives can have four or more disk platters in a sealed unit.
  6. In most of the disk units, the read/ write head does not touch the surface of the disk. Instead they are designed to float from 0.5 to 1.25 millionth of an inch from the disk surface. (Flying head design). Because the heads float so close to the sensitive disks, any contamination such as dust particle or hair, cause a head crash or a disk crash, which destroys some or all the data on the disk. Therefore hard disks are handled under sterile conditions.
  7. Hard disk technology was introduced by IBM (1970) since then they have become the most necessary memory hungry software.