STORAGE

Differentiate between storage and memory

Memory, which is composed of one or more chips on the motherboard, is a temporary holding place for data and instructions during processing. The contents of volatile memory, such as RAM, are lost when the power to the computer is turned off. The contents of nonvolatile memory, such as ROM, are not lost when power is removed from the computer.

Storage holds items such as data, instructions, and information for future use; that is, storage holds these items while they are not being processed. Storage is nonvolatile, which means the items in storage are retained even when power is removed from the computer. Compared to memory, the access time (the time it takes to locate a single item) for storage is slow.

Identify various types of storage media and storage devices

A storage medium (media is the plural) is the physical material on which items are kept. A storage device is the computer hardware that records and retrieves items to and from a storage medium. Storage devices can function as sources of input and output.

When storage devices transfer items from a storage medium into memory – a process called reading – they function as sources of input.

When storage devices transfer items from memory to a storage medium – a process called writing – they function as sources of output.

Types of storage media include floppy disks, hard disks, compact discs, tape, PC Cards, microfilm, and microfiche.

Explain how a floppy disk stores data

A floppy disk is a portable, inexpensive storage medium that consists of a thin, circular, flexible plastic disk with a magnetic coating enclosed in a square-shaped plastic shell. A floppy disk drive (FDD) is a device that can read from and write on a floppy disk. When you insert a floppy disk into a floppy disk drive, a shutter on the disk’s plastic shell slides to the side to expose the disk’s recording surface. A floppy disk is a type of magnetic media because it uses magnetic patterns to store items.

Data is stored in tracks and sectors. A track is a narrow recording band that forms a full circle on the surface of the disk. The disk’s storage locations consist of pie-shaped sections, which break the track into small arcs called sectors. For reading and writing purposes, sectors are grouped into clusters. A cluster consists of two to eight sectors and is the smallest unit of space used to store data. Formatting is the process of preparing a disk for reading and writing.

Identify the advantages of using high-capacity disks

A high-capacity disk drive is a disk drive that uses disks with capacities of 100 MB and greater (remember, a typical floppy disk can store only up to 1.44 MB). High-capacity disks are used to store large graphics, audio, or video files and for backup. A backup is a duplicate of a file, program, or disk that can be used if the original is lost, damaged, or destroyed.

Three high-capacity disk drives are the SuperDisk™ drive, the HiFD™ drive, and the Zip® drive.

The SuperDisk™ drive reads from and writes on a 120 MB or 250 MB SuperDisk™.

The HiFD™ (High-Capacity FD) drive reads from and writes on a 200 MB HiFD™ disk.

The Zip® drive is a high-capacity disk drive that uses a Zip® disk. The Zip® disk is larger and thicker than a 3.5-inch floppy disk and can store 100 MB or 250 MB of data.

Describe how a hard disk organizes data

A hard disk, or hard disk drive, consists of several inflexible, circular platters that store items electronically. A platter in a hard disk is made of aluminium, glass, or ceramic and is coated with a material that allows items to be recorded magnetically on its surface. Each platter has two read/write heads, one for each side. Because of the stacked arrangement of the platters, the location of the read/write heads often is referred to by its cylinder, which is the location of a single track through all platters. Some computers improve hard disk access time by using a disk cache, which is a portion of memory that the processor uses to store frequently accessed items. A hard disk can be divided into separate areas, called partitions, each of which functions as if it were a separate hard disk drive.

Identify the advantages of using an Internet hard drive

An Internet hard drive is a service on the Web that provides storage to computer users. People use Internet hard drives to:

Eliminate the need to transport files when away from a desktop computer

Instantaneously save large audio, video, and graphics files when surfing the Web

Make audio files, video clips, or pictures available to family, friends, co-workers, and customers

Immediately view time-critical data and images while away from a main office or location

Store offsite backups of data

Explain how a compact disc stores data

A compact disc (CD) is a flat, round, portable metal storage medium that usually is 4.75 inches in diameter and less than one-twentieth of an inch thick. Compact discs store items using microscopic pits (indentations) and land (flat areas) that are in the middle layer of the disc. A high-powered laser light creates the pits in a single track, divided into evenly spaced sectors, that spirals from the centre to the edge of the disc. A low-powered laser reads items by reflecting light off the disc surface. The reflected light is converted into a series of bits that the computer can process.

Understand how to care for a compact disc

With proper care, a compact disc is guaranteed to last five years, but could last up to 50 years. Compact discs should not be stacked or exposed to excessive heat, cold, sunlight, or contaminants. A compact disc should be held by its edges (do not touch the underside of the disc) and placed in its protective case, called a jewel box, when it is not being used. You can clean the bottom surface with a soft cloth and warm water or a specialized CD cleaning kit, and you can repair scratches on the bottom surface with a specialized compact disc repair kit.

Differentiate between CD-ROMs, CD-RWs, and DVD-ROMs

A CD-ROM, or compact disc read-only memory, is a compact disc that uses the same laser technology as audio CDs. For a computer to read items stored on a CD-ROM, you insert the disc into a CD-ROM drive or CD-ROM player. When viewing animation or video, the speed of a CD-ROM drive, or data transfer rate, is important. A higher the data transfer rate, results in smoother playback of images and sounds.

Most standard CDs are single-session because manufacturers record (write) all items to the disc at one time. Variations of standard CD-ROMs, such as PhotoCD, CD-R (compact disc-recordable), and CD-RW (compact disc-rewritable), are multisession, which means additional data, instructions, and information can be written at a later time.

A PhotoCD is a compact disc that contains digital photographic images.

A CD-R (compact disc-recordable) is a multisession compact disc onto which you can record your own items.

A CD-RW (compact disc-rewritable) is an erasable disc you can write on multiple times.

A DVD-ROM (digital video disc-ROM) is an extremely high-capacity compact disc capable of storing from 4.7 GB to 17 GB. In order to read a DVD-ROM, you must have a DVD-ROM drive. You also can obtain recordable and rewritable versions of DVD.

A DVD-R (DVD-recordable) allows you to write on it once and read (play) it many times.

With the new rewritable DVD, called a DVD+RW, you can erase and record on the disc multiple times.

Identify the uses of tape

Tape, one of the first storage media used with mainframe computers, is a magnetically-coated ribbon of plastic capable of storing large amounts of data and information at low cost. Because it requires sequential access, or consecutive reading and writing of data, tape is used for long-term storage and backup. (Floppy disks, hard disks, and compact discs all use direct access, which means you can locate a data item immediately, without having to move through all the items stored in front of it.)

Understand how an enterprise storage system works

An enterprise storage system is a strategy that focuses on the availability, protection, organization, and backup of storage in a company. To implement an enterprise storage system, a company uses a combination of techniques.

·         A server stores items needed by users on a network. A RAID system ensures that data is not lost.

·         A tape library is a high-capacity tape system that works with multiple tape cartridges for storing backups of data, information, and instructions.

·         A CD-ROM jukebox holds hundreds of CD-ROMs that can contain application programs and data.

·         An Internet backup can store data, information, and instructions on the Web.

·         A network attached storage (NAC) is an easy way to add hard disk space to a network.

·         A storage area network (SAN) is a high-speed network that connects storage devices.

Explain how to use PC Cards and other miniature storage media

A PC Card is a thin, credit card-sized device that fits into a PC Card slot on a notebook or personal computer. PC Cards are used to add storage, memory, communications, and sound capabilities.

A smart card stores data on a thin microprocessor embedded in a card similar in size to an ATM card. Two types of smart cards exist: intelligent and memory.

An intelligent smart card contains a processor and has input, process, output, and storage capabilities.

A memory card has only storage capabilities.

Identify uses of microfilm and microfiche

Microfilm and microfiche store microscopic images of documents on roll or sheet film. Microfilm uses a 100- to 215-foot roll of film. Microfiche uses a small sheet of film, usually about four inches by six inches. Libraries and large organizations use microfilm and microfiche to archive relatively inactive documents and files.