OS Disk Hardware

This tutorial of disk hardware describes briefly about the following disk hardware:

  • Magnetic disks
  • RAID
  • CD-ROM
  • CD-Recordable
  • CD-Rewritable
  • DVD

Magnetic Disks

Magnetic disks are organised into cylinders where each one containing as many tracks as there are heads stacked vertically. And the tracks are again divided into sectors.


RAID stands for Redundant Array of Inexpensive Disks.

The basic idea behind Redundant Array of Inexpensive Disks is just to install a box full of disks next to the computer, typically a large server, replace the disk controller card with a RAID controller, copy the data over to the RAID and then continue the normal operation.

In other word, you can say that RAID looks like a SLED (Single Large Expensive Disk) to the OS.

But RAID have better performance and reliability than SLED.


In the year of 1980, major two company namely Philips and Sony, together developed the Compact Disk (CD) which rapidly replaced 33 1/3-rpm vinyl record for music.

All the compact disks are 120mm across and 1.2mm thick, with a 15mm hole in the middle of the CD.

Now, after almost 4 years, that is, in the year of 1984, these two company now realised the power and potential of using the compact disks to store the computer data, therefore they developed CD-ROM, that stands for Compact Disk-Read Only Memory.


Physically, CD-Recordable (CD-R) stars with 120mm polycarbonate blanks that are like CD-ROMs, except that they contain a 0.6mm wide groove to guide the laser for writing.


After the people's demand for a rewritable CD-ROM, a technology was developed named CD-ReWritable (CD-RW), that uses the same size media as CD-Recordable (CD-R).

But, CD-RW uses an alloy of silver, antimony, indium, and tellurium for the recording layer.


DVD stands for Digital Video Disk or Digital Versatile Disk.

DVD uses the same general design as of CD with 120mm injection-moulded polycarbonate disks containing pits and lands that are illuminated by a laser diode and read by a photodetector.

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