Hard Disk Drives
Secondary Storage Device

Hard Disk as Secondary Storage Device

Hard disks are the faster storage capabilities than diskettes. The hard disks are permanently inside the computer and are not removable. Hard disk is also called direct access storage devices. The input and output device transfers data to the hard disk and is the hard disk drive. The hard disks can be used to store information.

The storage capacity of hard drives is measured in megabytes. Common sizes for personal computers range from 100MB to 500MB of storage. Each 10MB of storage is equivalent to approximately 5,000 printed pages. A hard disk uses rigid rotating platters. The platter has a planar magnetic surface on which digital data may be stored. Information is written to the disk by transmitting an electromagnetic flux through an antenna or read-write head that is very close to a magnetic material, which in turn changes its polarization due to the flux.

The information can be read by a read-write head because the magnetic fields cause electrical change in the read-write head as it passes over a platter. A hard disk drive consists of a central axis which has the platters spin at a constant speed. The armature moves the heads radically across the platters as they spin, allowing each head access to the entirety of the platter.

The movement of the armature and the rotation of the disk, and perform reads and writes on demand from the disk controller. Modern drive electronics are capable of scheduling reads and writes efficiently across the disk and remapping sectors of the disk which have failed. The disk surface and the drive's internal environment must be kept clean to prevent damage from fingerprints, hair, dust, smoke particles, etc. Most of the modern drives include temperature sensors and their operation to the operating environment.

The hard disk with the platter can be removed. Hard disk drives are not airtight. You can see these breather holes on all drives -- they usually have a warning sticker next to them, informing the user not to cover the holes. The air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning disk platters. The hard disks can be used to store information.

The storage capacity of hard drives is measured in megabytes. Due to the extremely close spacing of the heads and disk surface, any contamination of the read-write heads or disk platters can lead to a head crash & a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film. The platter has a planar magnetic surface on which digital data may be stored.

Information is written to the disk by transmitting an electromagnetic flux through an antenna or read-write head that is very close to a magnetic material, which in turn changes its polarization due to the flux. Consequently, hard disks can store much more data than floppy disk, and access and transmit it faster. In 2005, a typical workstation hard disk might store between 80 GB and 400 GB of data, rotate at 7,200 to 10,000 rpm, and have a sequential transfer rate of over 50 MB/s.

The fastest workstation hard drives spin at 15,000 rpm. Notebook hard drives, which are physically smaller than their desktop counterparts, tend to be slower and have less capacity. Most spin at only 4,200 rpm or 5,400 rpm, though the newest top models spin at 7,200 rpm.

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