If you recollect the block diagram of computer you studied in your lower grades, the CPU consists of three basic units: The Memory Unit, The Control Unit and The Arithmetic and Logic Unit (ALU).

All the three units are essential for the functioning of computers. In this article we discuss about the Hard Disk Drives and the role they play in forming an integral part of memory unit.

This is what a Hard Disk Drive exactly is:

The Hard Disk Drive abbreviated as HDD is the main and largest storage device of the computer. It involves electronic circuitry and moving parts to store data by using the magnetic polarities. The data the hard disk drives store is permanent and is present even if the computer is turned off.

The American data storage companies Seagate Technologies and Western Digital, Hitachi and Toshiba are the leading producers of hard disk drives.

This is how a Hard Disk Drive is constructed :

After it was introduced in 1956, the internal construction of HDDs hasn’t changed much except that it is manufactured in various form factors (dimensions).

It basically consists of hard drive platters (disk shaped magnetic material) inside air sealed casing.

From the inside, one side of the casing is the electronics control board called disk controller. There is also a motor which spins the platters at 3600 or 7200 rpm beneath the board.

The arm present over the platter in the corner holds the read (or) write heads and has extremely fast moving patterns.

Connection Architecture:

These hard drives are connected to the motherboard using the power cable and either of the ATA, SATA or SCSI cables via the back end ports. The exact cable to b used will depend on the type of HDD and usually included with the HDD.

Also See: Best Hard Disk Drives of 2014

This is How The Hard Disk Drives Work:

Actually the files on the hard drive are all scattered on the platter in sectors and tracks. (Tracks are concentric circles, and the pie-shaped wedges present on each track are called sectors.) Also the data flow control from and into the Hard Drive is controlled by the operating system.

It decides how the components have to move within the drive to perform a specific operation and relies on the disk controller to implement it by controlling the hardware.

Initially, the operating system based on its analysis over the hard drives File Allocation Table (FAT) communicates with the disk controller.

The read (or) write head present on the arm has to move onto different sectors to check for required files or areas available for storage.

And this movement of the arm is taken care of by the disk controller based on the instructions the operating system provides it. All of the information is then stored or written magnetically.

For instance, if the computer plans to read information present in the hard drive, it considers the magnetic polarities on the platter. These magnetic polarities are interpreted as 1’s and 0’s and read by the computer.

NOTE: You could open a defunct Hard Disk Drive to understand the working much better. But remember that if you open the casing of a working Hard Disk Drive then it won’t work the next time you connect it to the computer.

Also See: What Formatting your Hard Disk Drive means?