Even before the first computer was conceptualized, data had already beenstored on hard copy medium and used with a machine. As early as 1801, thepunched card was used as a control device for mechanical looms. One andone-half centuries later, IBM joined punched cards to computers, encodingbinary information as patterns of small rectangular holes. Today, punchcards are rarely used with computers. Instead, they are used for a handfulof train tickets and election ballots.
Although some may find itsurprising, a computer printout is another type of hard copy medium. Pictures, barcodes, and term papers are modern examples of data storagethat can later be retrieved using optical technology. Although itconsumes physical space and requires proper care, non-acidic paperprintouts can hold information for centuries. If long-term storage is notof prime concern, magnetic medium can retain tremendous amounts of dataand consume less space than a single piece of paper.
The magnetic technology used for computer data storage is the sametechnology used in the various forms of magnetic tape from audiocassetteto videocassette recorders. One of the first computer storage devices wasthe magnetic tape drive. Magnetic tape is a sequential data storagemedium. To read data, a tape drive must wind through the spool of tape tothe exact location of the desired information.
To write, the tape driveencodes data sequentially on the tape. Because tape drives cannot randomlyaccess or write data like disk drives, and are thus much slower, they havebeen replaced as the primary storage device with the hard drive. The harddrive is composed of thin layers of rigid magnetic platters stacked on topof one another like records in a jukebox, and the heads that read andwrite data to the spinning platters resemble the arm of a record player. Floppy disks are another common magnetic storage medium.
They offerrelatively small storage capacity when compared to hard drives, but unlikehard drives, are portable. Floppy disks are constructed of a flexibledisk covered by a thin layer of iron oxide that stores data in the form ofmagnetic dots. A plastic casing protects the disk: soft for the 51/4-inchdisk, and hard for the 31/2-inch disk. Magnetic storage medium, for allits advantages, only has a life expectancy of twenty years. Data can be stored on electronic medium, such as memory chips.
Everymodern personal computer utilizes electronic circuits to hold data andinstructions. These devices are categorized as RAM (random access memory)or ROM (read-only memory), and are compact, reliable, and efficient. RAMis volatile, and is primarily used for the temporary storage of programsthat are running. ROM is non-volatile, and usually holds the basicinstruction sets a computer needs to operate. Electronic medium issusceptible to static electricity damage and has a limited lifeexpectancy, but in the modern personal computer, electronic hardwareusually becomes obsolete before it fails. Optical storage medium, on theother hand, will last indefinitely.
Optical storage is an increasingly popular method of storing data. Optical disk drives use lasers to read and write to their medium. Whenwriting to an optical disk, a laser creates pits on its surface torepresent data. Areas not burned into pits by the laser are called lands. The laser reads back the data on the optical disk by scanning for pits andlands.
There are three primary optical disk mediums available for storage:CD-ROM (compact disc read-only memory), WORM (write once read many), andrewritable optical disks. The CD-ROM is, by far, the most popular form ofoptical disk storage; however, CD-ROMs are read-only. At the factory,lasers are used to create a master CD-ROM, and a mold is made from themaster and used to create copies. WORM drives are used almost exclusivelyfor archival storage where it is important that the data cannot be changedor erased after it is written, for example, financial record storage.
Rewritable optical disks are typically used for data backup and archivingmassive amounts of data, such as image databases. Although there are many manufacturers of the data storage devices used inthe modern personal computer, each fits into one of four technologicalclasses according to the material and methods it uses to recordinformation. Hardcopy medium existed before the invention of thecomputer, and magnetic medium is predominantly used today. Electronicmedium is used by every computer system, and is used to store instructionsor temporarily hold data.
Finally, optical storage medium utilizes lasersto read and write information to a disk that lasts indefinitely. .
