• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

Our editors will evaluation what you’ve submitted and decide whether or not to revise the article. Auxiliary memory items are amongst pc peripheral equipment. They commerce slower entry charges for greater storage capacity and knowledge stability. Auxiliary memory holds packages and information for future use, and, as a result of it is nonvolatile (like ROM), it's used to retailer inactive programs and to archive information. Early types of auxiliary storage included punched paper tape, punched playing cards, and magnetic drums. Because the 1980s, the commonest forms of auxiliary storage have been magnetic disks, magnetic tapes, and optical discs. Magnetic disks are coated with a magnetic materials such as iron oxide. There are two types: onerous disks made of inflexible aluminum or glass, and removable diskettes manufactured from versatile plastic. In 1956 the first magnetic onerous drive (HD) was invented at IBM; consisting of fifty 21-inch (53-cm) disks, it had a storage capability of 5 megabytes.

By the nineteen nineties the usual HD diameter for PCs had shrunk to 3.5 inches (about 8.9 cm), with storage capacities in excess of a hundred gigabytes (billions of bytes); the usual size HD for portable PCs ("laptops") was 2.5 inches (about 6.4 cm). Since the invention of the floppy disk drive (FDD) at IBM by Alan Shugart in 1967, diskettes have shrunk from eight inches (about 20 cm) to the current customary of 3.5 inches (about 8.9 cm). Laborious drives usually have several disks, or platters, with an electromagnetic read/write head for each surface; the whole assembly is known as a comb. A microprocessor within the drive controls the movement of the heads and also contains RAM to store knowledge for transfer to and from the disks. The heads transfer across the disk surface because it spins as much as 15,000 revolutions per minute; the drives are hermetically sealed, Memory Wave allowing the heads to float on a thin movie of air very close to the disk’s floor.

A small current is applied to the pinnacle to magnetize tiny spots on the disk surface for storage; equally, magnetized spots on the disk generate currents in the pinnacle as it moves by, enabling information to be learn. FDDs function similarly, however the removable diskettes spin at only some hundred revolutions per minute. Information are saved in shut concentric tracks that require very precise management of the learn/write heads. Refinements in controlling the heads have enabled smaller and closer packing of tracks-up to 20,000 tracks per inch (8,000 tracks per cm) by the start of the twenty first century-which has resulted in the storage capability of these devices growing nearly 30 % per 12 months because the 1980s. RAID (redundant array of inexpensive disks) combines a number of disk drives to store information redundantly for higher reliability and faster entry. They're used in excessive-efficiency laptop community servers. Magnetic tape, just like the tape utilized in tape recorders, has also been used for auxiliary storage, primarily for archiving knowledge.

Tape is cheap, however entry time is way slower than that of a magnetic disk as a result of it's sequential-entry memory-i.e., knowledge should be sequentially read and written as a tape is unwound, relatively than retrieved immediately from the desired level on the tape. Servers may use giant collections of tapes or optical discs, with robotic units to select and load them, slightly like old-fashioned jukeboxes. One other type of largely read-solely memory is the optical compact disc, developed from videodisc know-how throughout the early 1980s. Information are recorded as tiny pits in a single spiral monitor on plastic discs that vary from 3 to 12 inches (7.6 to 30 cm) in diameter, though a diameter of 4.8 inches (12 cm) is most common. The pits are produced by a laser or by a stamping machine and are learn by a low-energy laser and a photocell that generates an electrical sign from the varying light mirrored from the sample of pits.

Optical discs are removable and have a far greater memory capability than diskettes; the most important ones can retailer many gigabytes of information. A common optical disc is the CD-ROM (compact disc learn-only Memory Wave Protocol). It holds about 700 megabytes of knowledge, recorded with an error-correcting code that can right bursts of errors brought on by dust or imperfections. CD-ROMs are used to distribute software, encyclopaedias, and Memory Wave Protocol multimedia textual content with audio and images. CD-R (CD-recordable), or WORM (write-once read-many), is a variation of CD-ROM on which a user could record info but not subsequently change it. CD-RW (CD-rewritable) disks could be re-recorded. DVDs (digital video, or versatile, discs), developed for recording films, store data more densely than does CD-ROM, with extra highly effective error correction. Though the identical measurement as CDs, DVDs sometimes hold 5 to 17 gigabytes-several hours of video or a number of million text pages. Magneto-optical discs are a hybrid storage medium. In studying, Memory Wave spots with totally different instructions of magnetization give completely different polarization within the reflected gentle of a low-energy laser beam. In writing, each spot on the disk is first heated by a powerful laser beam after which cooled below a magnetic area, magnetizing each spot in one route, to retailer all 0s. The writing process then reverses the path of the magnetic area to store 1s the place desired.