Hard Disk.

Technically microcomputer hard disks are called Winchester disks or fixed disks as they are a pack of disks permanenetly sealed inside a disk drive. The sealed case contains platters fixed in place, read/write heads and other part of mechanisms. It overcomes much of the danger of dust, magnetism and finger prints interfering with the data. The read/write heads do not actually touch the surface of the disk (as in floppy disk drives) but fly over it on a cushion of air.

Like floppy disks the older types were of 5¼" diameter and the newer are 3½". Fixed disks spin at an average 3,600rpm (equivalent to 150 km/hr) and, unlike floppy disks, they spin continuously. This means faster reading and writing than floppy disks (about 300,000 bytes/sec) as there is no wait until the disk accelerates to required speed and the waiting time for the required sector to pass under the read/write head is dramatically reduced.

Fixed disks have much greater capacity than floppy disks. Originally microcomputer hard disks held 10M, but todays hard disks capacities are measured in gigabytes. The increased capacity is in part because of the metal surface, in part because they are sealed inside a case and in part because the disks are multi-layered.

To connect a hard disk to a microcomputer, a hard disk controller card must be installed on the motherboard. This card includes circuitry that serves as an interface between the motherboard and the hard disk. The circuitry must conform to standards. Two most common standards today are Small Computer System Interface (SCSI) and Integrated Drive Electronics (IDE). The IDE standard has a size limit of 528M which is too small for modern PCs. EIDE superceeded IDE and has increased the maximum size allowing up to 4 hard drives to be connected at once.

It is possible to have more than one hard disk inside your computer. In this case the main dis k is called master, and the second is called slave.

Invention of hard disks certainly eliminated the difficulties faced by microcomputer users of a few years ago of having to locate and insert a number of different floppy disks whenever they wished to use their computer.

The disadvantage of storing everything on a hard disk is that data, if not programs, is often required to be transferable between computers. In consequence, floppy disks retain value as a means of moving data. But on the other hand modern files are often bigger than a floppy disk can hold. So new technologies like zip drive and jaz drive appeared on the market.