Disk Drives

The computer loads a program from a disk into the RAM. Hard disks usually spin at 3600 or more revolutions per minute and floppies run at 300 RPM. The hard disk can hold more information than a floppy, and give it to you much faster, but their principal of operation is the same.

The surfaces of a disk are coated or plated with a magnetic metal. A small recording head is placed very near each surface. The head can be moved in and out along the radius of the disk, so that it can read or write along any of many tracks, called cylinders.

If you move a magnet past a wire, an electric current is generated. This is also how disks work. Spots on the disks are magnetized, representing bits of bytes. As the disk spins by a small coil in the head, as the spots pass, spikes of electricity are produced. These spikes are translated into bytes and passed to the CPU and the RAM.

If you run a current through a wire near a ferrous metal, the metal will become magnetized. This is how writing to a disk is done. As the disk turns past the coil in the head, the coil is energized every time an "on" bit is to be written to the disk, resulting in a magnetized spot. The switching on and off of the electricity flowing through the head is very fast.

These are both called "floppies" although the one on the right is rock hard. The reason is that the one on the right has a floppy disk inside the case.

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