Hard disks are rigid metal platters that hold data as magnetized spots.

Switching from a microcomputer that uses only diskettes to one containing a hard disk is like discovering the difference between moving your household in several trips in a small sports car and doing it all at once with a moving van. Whereas a high-density 3½-inch diskette holds 1.44 megabytes of data a hard disk in the personal computer may hold 40, 80 100, 200, 500 megabytes, or a gigabyte or more. Indeed, at first with a hard disk you may feel you have more strange capacity than you will ever need. However, after a few months, you may worry that you didn’t have enough. This feeling may be intensified if you using graphics-oriented programs, with pictures and other features requiring immense amounts or storage.

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Diskettes are made out of flexible material, which makes them ‘’floppy’’ by contrast, a hard disk is thin but rigid metal platters covered with a substance that allows data to be held in the form of magnetized spots. Hard disks are also tightly sealed within an enclosed unit to prevent by foreign matter from getting inside. Data may be recorded on both sides of the disk platters.
Well now describe the following aspects of hard disk technology:
# Microcomputer hard disk drives
# Microcomputer hard disk variations
# hard disk technology for large computer systems

Microcomputer hard disk drives

In microcomputers’ hard disks are not more platters sealed inside hard disk drives that are built into the system unit and cannot be removed. The drive is installed in a drive bay, a slot or opening in the computer cabinet. From the outside of a microcomputer, a hard disk drive is nit visible it looks simply like part of the front panel on the system cabinet inside however is s disk or disks on a drive spindle, read-write heads mounted on an actuator (access) arm that moves back and forth, and power connections and circuitry. (see figure 4.12.) the disks may be 5¼ Inches in diameter, although today they are more often 3 ½ inches with some even smaller.

Microcomputer hard disk variations: power and portability

If you have an older microcomputer or one with limited capacity in its existing hard disk, some variations are available that can provide additional power or portability:
# Miniaturization: newer hard disk drives are less than half the height of older drives (1 ½ inches high) and so are called half-bright. Thus you could fit two disk drives into the bay in the system cabinet formerly occupied by one.
   In addition, the diameter of the disks has been getting smaller. Instead of 5¼ or 3 ½ inches, some platters are 2.5 1.8 or even 1.3 inches in diameter. The half-dollar-size 1.3 inch Kitty Hawk microdisk, which is actually designed for use in handheld computers, holds 21 megabytes of data.
# External hard disk drives: if you didn’t have room in the system unit for an internal hard disk but need additional strong, consider adding an external hard disk drive, some detached external hard drives, which have their own power supply, can store gigabytes of data.

# hard disk cartridges: the disadvantages of hard disk include the difficulty if removing them and their finite amount of strong. Hard disk cartridges consist of one or two platters enclosed along with read/write heads in a hard plastic case. The case is inserted into a detached external cartridge system connected to a microcomputer. A cartridge which is removable and easily transported in a briefcase may hold as much as 1.2 gigabytes of data. An additional advantage of hard disk cartridges is that they may be used for backing up data.

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