|
The disk spinning apparatus is referred to as a disk drive. Every disk drive is composed of one or more read/write heads that, hence the name, read and scrawl data . A disk's access time is not as quick as retrieving data from main disks, however disks are much less expensive. Unlike the RAM, disks preserve data even when a computer is turned completely off. Consequently, disks are considered the storage medium of choice for most categories of data. Magnetic tape is another storage medium. Tapes are used almost exclusively for archiving and backup because of their sequential-access device nature. To access data in the median of a tape requires the tape drive to pass through all the previous data. A new disk is called a blank disk which has no data stored on it. Before you can input data on a so-called blank disk you must first format it. Data is encoded with microscopic magnetized needles on magnetic disks. You can erase and save data numerous times on a magnetic disk. Magnetic disks come in various forms suck as the hard disk and the floppy disk. Optical disks on the otherhand record its data by burning microscopic holes on the disk's surface using a laser. Reading the disk requires another laser to detect the holes by changing its reflection pattern. Optical disks include erasable eo's or eraseble opticals such as the cd and dvd drive. Disk drives are either internally housed in the computer or externally housed in a box that is separate from the computer. An optical disk or CD, compact disc, is a polycarbonate with one or several metal layers able to store digital information. The most common types of CDs are CD-Roms which compile computer data and those used by the music industry to save digital recordings. These types of compact disks, however, are read-only meaning that once the data has been burned or recorded onto them, they can only be played or read. CD-Rs and CD_RWs, on the otherhand, are capable of having their data overwritten and erased by neoteric data. The new DVD-Rs and DVD-RWs even store up to 4.7 Gb pushing optical disks to another dimension. Erasable optical storage is currently too laggard for a computer's chief storage facility. As the prices are dropping and the speed heightens, optical storage devices such as the CD=Rs and DVD-Rs are assuming a more popular alternative to the old tape systems for backup method. A soft magnetic disk is called a floppy. Unlike most hard disks, floppy disks are portable because one can remove them from a disk drive and reuse them at a later time. Disk drives used for floppy are called floppy drives and are saved on the A drive. Floppy disks are slower to access than hard disks and contain less storage capacity (approximately 1.2Mb), but are much cheaper. And most impressively, they are portable. Unlike their cousin the 5 ¼ inch disk, the 3 ½ inch floppy disk is high density and stores up to 1.44Mb at 720K. The mechanism writing and reading data on a hard disk is the hard disk drive (HDDs) or just hard drive. Hard drives for PCs most commonly have seek times of roughly 12 milliseconds or less. Many disk drives enhance their performance by a technique commonly called caching, or storing in a fast storage buffer within the computer's CPU. There are several interface standards by which data is transmitted between the computer and a hard disk. The most general being the SCSI and IDE. Winchester, in 1973, was one of the very first popular hard disk drive technologies invented by IBM. SCSI is short for small computer system interface. SCSI is a parrelel system interface utilized by UNIX systems, Apple Macintosh computers and many PCs for attaching peripheral devices (such as printers and disk drives) to computers. SCSI interfaces impliment faster data transmission rates (up to and including 80 megabytes per second) than standard parallel and serial ports. One can attach numerous devices to a single SCSI port, making SCSI really an I/O bus rather than a simple interface. While SCSI is the standard interface for Macintoshes, the new iMac comes with an IDE, a less costly interface, in which the controller is housed in the CD-ROM or disk drive. Other interfaces supported by PCs include Centronicas for printers and ESDI and enhanced IDE for mass storage devices. You can attach SCSI devices to a PC by simply inserting a SCSI board in an expansion slot. Last but not least is RAID, the acronym for Redundant Array of Inexpensive or Independemt Disks. It is a disk drive that employs two or more drives in conjunction for performance and fault tolerance. RAID disk drives aren't generally necessary for PCs but are used quite extensively by servers. There are various RAID levels. The most common being 0, 3, and 5: Level 0 allows data striping or spreading out blocks from each file along multiple disks but not redundant. This tolerance in conjunction. And Level 5 provides stripe error correction information and data stripping hones performance however lacks fault tolerance. Level 3 is the same as Level 0, except reserves one dedicated disk for the error correction of data. It provides some fault at the byte level. This results in unmatched fault tolerance and high performance. |
