Fundamentals of Computer Hard Drive

One of the permanent storage types, the computer hard drive is the primary storage device used in computers or laptops. Commonly abbreviated as HDD, it is used to store the operating systems, programs, media files, and documents whether you created them, copied them, or downloaded them from the internet.

The amount of data that you can store, depends on the capacity of a computer hard drive. The older models of hard drives used to have a storage capacity of Megabytes(MB) and the newer hard disk drives can store data up to several terabytes(TB).

Computer Hard Drive Sizes

• 3.5″ for Desktop Computers. The standard size for hard disk drives is 3.5” which was launched in 1983 with an introductory capacity of only 10 MB. The 3.5”m size hard disks are still used to date in desktop computers
• 2.5″ for Laptops. The 2.5 inches hard disk was invented by Prairie Tek in the year 1988. The first small-sized hard disk was designed for notebooks and the size of 1st 2.5” HDD was 20 MB.

HDD interface types

• 40 pin IDE male connector on the motherboard.
• 50-pin SCSI connector
• SATA connector
• USB connector.

Hard Drive Geometry

The hard disk works on the principle of magnetism. The data you save on the hard disk is actually saved on the circular shiny surface called a platter. This platter is divided into a number of smaller areas that get magnetized or demagnetized. The magnetism allows the data to stay on the platter even in the absence of power.

The data is stored in the form of bits along the circular tracks on the platter. These tracks are further divided into smaller areas called sectors. A map (File allocation table) of the used sectors is copied to the hard drive and provides the necessary information to the system about the free sectors available. The tracks, when grouped together are called cylinders.

As compared to a floppy disk drive where the data is stored on a single disk, a hard drive can contain as many numbers of platters depending on its storage capacity. Similarly, the FDD has a single head whereas the number of heads present in the HDD depends on the number of platters inside the hard disk drive. The number of heads will be double the number of platters since a single platter will have heads on both sides.

On the right side, you can see the picture of the actual hard disk from inside after opening its enclosure. The electromagnetic head is mounted on the actuator arm which moves as per the directions from the hard disk controller. Since the data is stored on the platter at different locations, the head shifts through various parts on the platter to fetch or write the data. The platter rotates at a speed determined in RPM(rotations per minute). Computer hard drives have different speeds like 5400 RPM or 7200 RPM.

“Warning: The hard disk should be opened in air-tight rooms only by professionals. We have opened a damaged hard disk to show you the inner view of the hard drive.”