<hardware, storage> (Or "hard disk drive", "hard drive", "floppy disk drive", "floppy drive") A peripheral device that reads and writes hard disks or floppy disks. The drive contains a motor to rotate the disk at a constant rate and one or more read/write heads which are positioned over the desired track by a servo mechanism. It also contains the electronics to amplify the signals from the heads to normal digital logic levels and vice versa. In order for a disk drive to start to read or write a given location a read/write head must be positioned radially over the right track and rotationally over the start of the right sector. Radial motion is known as "seeking" and it is this which causes most of the intermittent noise heard during disk activity. There is usually one head for each disk surface and all heads move together. The set of locations which are accessible with the heads in a given radial position are known as a "cylinder". The "seek time" is the time taken to seek to a different cylinder. The disk is constantly rotating (except for some floppy disk drives where the motor is switched off between accesses to reduce wear and power consumption) so positioning the heads over the right sector is simply a matter of waiting until it arrives under the head. With a single set of heads this "rotational latency" will be on average half a revolution but some big drives have multiple sets of heads spaced at equal angles around the disk. If seeking and rotation are independent, access time is seek time + rotational latency. When accessing multiple tracks sequentially, data is sometimes arranged so that by the time the seek from one track to the next has finished, the disk has rotated just enough to begin accessing the next track. See also sector interleave. The disks may be removable disks; floppy disks always are, removable hard disks were common on mainframes and minicomputers but less so on microcomputers until the mid 1990s(?) with products like the Zip Drive. A CD-ROM drive is not usually referred to as a disk drive. Two common interfaces for disk drives (and other devices) are SCSI and IDE. ST-506 used to be common in microcomputers (in the 1980s?). (1997-04-15)

Disc integration, also known in integral calculus as the disc method, is a method for calculating the volume of a solid of revolution of a solid-state material when integrating along an axis "parallel" to the axis of revolution. This method models the resulting three-dimensional shape as a stack of an infinite number of discs of varying radius and infinitesimal thickness.

(disk drives)

disc

Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism.

Disk Clean-up (cleanmgr.exe) is a computer maintenance utility included in Microsoft Windows designed to free up disk space on a computer's hard drive.

floppy disk

<hardware, storage> (Or "floppy", "diskette") A small, portable plastic disk coated in a magnetisable substance used for storing computer data, readable by a computer with a floppy disk drive. The physical size of disks has shrunk from the early 8 inch, to 5 1/4 inch ("minifloppy") to 3 1/2 inch ("microfloppy") while the data capacity has risen. These disks are known as "floppy" disks (or diskettes) because the disk is flexible and the read/write head is in physical contact with the surface of the disk in contrast to "{hard disks}" (or winchesters) which are rigid and rely on a small fixed gap between the disk surface and the heads. Floppies may be either single-sided or double-sided. 3.5 inch floppies are less floppy than the larger disks because they come in a stiff plastic "envelope" or case, hence the alternative names "stiffy" or "crunchy" sometimes used to distinguish them from the floppier kind. The following formats are used on IBM PCs and elsewhere: Capacity Density Width 360K double 5.25" 720K double 3.5" 1.2M high 5.25" 1.44M high 3.5" Double denisty and high density are usually abbreviated DD and HD. HD 3.5 inch disks have a second hole in the envelope and an overlapping "HD" logo. (1996-08-23)