Slide 4.5: The cost of disk accesses Slide 4.7: Magnetic tapes Home

Floppy Disks

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A floppy disk is a small, portable plastic disk coated in a magnetisable substance used for storing computer data, readable by a computer with a floppy disk drive.

Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive. And most importantly, they are portable. The physical size of disks has shrunk from the early 8 inch, to 5¼ inch (“minifloppy”) to 3½ inch (“microfloppy”) while the data capacity has risen:

• 5¼-inch: The common size for PCs made before 1987. This type of floppy is generally capable of storing between 100K and 1.2MB of data. The most common sizes are 360K and 1.2MB.
• 3½-inch: Despite their small size, microfloppies have a larger storage capacity than their cousins—from 400K to 1.4MB of data. The most common sizes for PCs are 720K (double-density) and 1.44MB (high-density).

Conventional floppy drives contain the following basic components: A spindle clamping mechanism to hold the diskette in place as it spins;

• Either one or two magnetic read/write heads mounted on a mechanism that moves the heads radially across the diskette's surface; and
• A sensor that detects the rotational position of the diskette via an index hole (or magnetic sensor in 3½ inch drives) on floppy disks.