Chapter 7: Storage


  1. Differentiate between storage and memory
  2. Identify various types of storage media and storage devices
  3. Explain how a floppy disk stores data
  4. Identify the advantages of using high-capacity disks
  5. Describe how a hard disk organizes data
  6. Identify the advantages of using an Internet hard drive
  7. Explain how a compact disc stores data
  8. Understand how to care for a compact disc
  9. Differentiate between CD-ROMs, CD-RWs, and DVD-ROMs
  10. Identify the uses of tape
  11. Understand how an enterprise storage system works
  12. Explain how to use PC cards and other miniature storage media
  13. Identify uses of microfilm and microfiche

This chapter explains various storage media and storage devices. Students discover how memory is different from storage. Floppy disks are introduced, and characteristics of a floppy disk, floppy disk drives, care of floppy disks, and high-capacity floppy disks are presented. Hard disks are explained, and students find out about characteristics of a hard disk, how a hard disk works, removable hard disks, hard disk controllers, RAID, and maintaining data on a hard disk. Compact discs, including CD-ROMs and DVD-ROMs, are described. Finally, students learn about tapes, PC Cards, and other types of storage such as smart cards, microfilm and microfiche.

1 | 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.

2 | 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.

3 | 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.

4 | 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.

5 | 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 aluminum, 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.

6 | 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

7 | 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 center 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.

8 | 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.

9 | 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.

10 | 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.)

11 | 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.

12 | 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.

13 | 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.

Expand Your Knowledge

  1. Memory vs. storage
  2. Storage media and devices
  3. Floppy disks
  4. High-capacity disks
  5. Hard disks
  6. Advantages of an Internet Hard Drive
  7. Compact discs
  8. Caring for compact discs
  9. CD-ROMs, CD-RWs, and DVD-ROM
  10. Tape
  11. Enterprise storage systems
  12. PC cards and miniature storage media
  13. Microfilm and microfiche

Here you will find additional information that will expand and enhance your knowledge beyond that contained in your textbook. Compare this information to what may be provided in a traditional classroom by your instructor or peers.

1 | Memory Vs. Storage

In general, memory (RAM) is fast, short-term, and volatile. Storage, on the other hand, is slower, long-term, and nonvolatile. Like nonvolatile memory, the contents of storage are retained when a computer’s power is turned off. Unlike most nonvolatile memory, however, the contents of storage usually can be erased or changed.

2 | Storage Media And Devices

The first computer storage medium was a punched card. Herman Hollerith’s punched card tabulating machine helped complete the 1890 census in just 2½ years (compared to 8 years for the 1880 census) at a savings of more than $5 million. Hollerith later founded the Tabulating Machine Company, which eventually became known as International Business Machines (IBM). An understanding of storage terms is very important for purchasers, and users, of storage devices.

  • 1 Kilobyte (KB) ≈ 1 thousand bytes
  • 1 Megabyte (MB) ≈ 1 million bytes
  • 1 Gigabyte (GB) ≈ 1 billion bytes
  • 1 Terabyte (TB) ≈ 1 trillion bytes
  • 1 Petabyte (PB) ≈ 1 quadrillion bytes

1 KB stores approximately ½ page of text. Depending on speed and size, rough costs for RAM are about $40 to $50 per megabyte, while hard disk storage costs are around $0.20 per megabyte.

3 | Floppy Disks

Although the 5.25-inch floppy disk is physically larger, the storage capacity for a 5.25-inch floppy disk is less than for a comparable 3.5-inch floppy disk. Because of the 3.5-inch floppy disk’s greater durability and superior storage capacity, the 5.25-inch floppy disk at best can be considered a very endangered species. With its rigid plastic shell, it may be difficult to see the 3.5-inch disk as “floppy.” The name is justified, however, by the disk’s ancestry and the fact that, if the protective shell is removed, the disk on which the data is written is indeed floppy. Today, most new computers (although not the new Apple iMac) come with a 3.5-inch floppy disk drive; a few manufacturers still will, for a price, add a 5.25-inch floppy disk drive.

The procedure for formatting a floppy disk depends on the operating system. Floppy disks are soft-sectored, meaning that the number of sectors is not predetermined. The cluster concept creates an odd situation: one file with 100,000 bytes requires less disk space (about 25 clusters at 8 sectors per cluster and 512 bytes per sector) than 1,000 small files of 100 bytes each (1,000 clusters).

A floppy disk spins at about 300 revolutions per minute. When writing data, the floppy disk drive’s read/write head generates electronic impulses that change the magnetic polarity of areas along a track to represent the 1 or 0 bits being recorded. When reading data, the read/write head senses the magnetic areas that have been recorded.

4 | High-Capacity Disks

The three types of high-capacity disks were developed by three different manufacturers: SuperDisk™ is from Imation, HiFD™ is from Sony Electronics, Inc, and the Zip® drive is from Iomega.

Although manufacturers always are concerned about software piracy (unlawfully duplicating or distributing proprietary software), many recommend that users create a backup of programs before installing them on a computer. Backup guards against system failures, such as a head crash, and human errors, such as inadvertently deleting key files. If you ever accidentally delete a file, seek help immediately from a computer support person who sometimes can recover the “erased” file.

5 | Hard Disks

In the early 1980s, hard disk drives were called “Winchester” drives because they had two 30-megabyte disks, a characteristic reminiscent of the Winchester 30-30 rifle. In addition to making hard disks more efficient and allowing the installation of multiple operating systems, large hard disks may be partitioned to:

  • Limit software disasters (which usually are confined to one partition)
  • Shorten path lengths and assist in file keeping
  • Save keystrokes (operating systems usually return to the directory they left)
  • Enhance security (different partitions may warrant different safety levels)
  • Permit variable frequencies of backup
  • Allow unattended backups (smaller partitions may fit on a single tape)

Unlike floppy disk read/write heads, hard disk read/write heads do not touch the disk surface. Because of the close tolerance between the disk head and the rotating disk surface, hard disk drives are manufactured in an extremely clean setting, typically cleaner than a hospital operating room. Many hard disk drives are warranted for five years, but most warranties are prorated, meaning that if it fails in the first year it can be replaced at 20 percent of the original cost. All warranties are void, however, if the drive is opened, because contaminated air and dust render the drive unusable.

On a personal computer, a hard disk controller (HDC) is the interface for the hard disk. Many external hard drives use a USB port as their interface. Two other types of HDCs are the EIDE (Enhanced Integrated Drive Electronics) controller, which can support up to four hard disks, and SCSI (small computer system interface) controllers, which can support multiple disk drives as well as other peripherals. A removable hard disk is a disk drive in which a plastic or metal case surrounds the hard disk so that you can remove it from the drive. Two reasonably priced, removable hard disks are the Jaz® disk, which can store up to 2 GB, and the Peerless™ disk, which can store up to 20 GB.

A RAID (redundant array of independent disks) system integrates two or more hard disks, duplicating data, instructions, and information to improve data reliability.

6 | Advantages Of An Internet Hard Drive

When your computer’s hard disk is full, an Internet hard drive can provide additional storage space. Ease of use, number of features, and amount of storage space varies, based on the specific Internet hard drive Web site. Do you trust the security of online storage services? What types of information might you store online? What are other advantages and disadvantages of Internet hard drives?

7 | Compact Discs

Laser disks first were developed by RCA for showing home movies. The 14-inch optical disk was a derivative of these early 1980s video disks. Advantages that compact discs offer over hard disks include: greater data density, less expense (bit for bit), increased durability, and no head crashing.

8 | Caring For Compact Discs

Compare the proper care guidelines for using floppy disks (page 7.9) with the proper care guidelines for using compact discs (page 7.19). How are the guidelines similar? How are they different?

9 | CD-ROMs, CD-RWs, And DVD-ROM

On a computer, screen displays for software used to play audio CDs resemble typical CD players, but the controls are accessed with a pointing device. A single CD-ROM can store the entire Encyclopedia Britannica with room left over. You write on a CD-R using a CD recorder or a CD-R drive and special software. To write on a CD-RW disc, you must have CD-RW software and a CD-RW drive. A multiread CD-ROM drive can read audio CDs, data CDs, CD-Rs, and CD-RWs.

On one side, a DVD-ROM can store up to 13 times the amount of information that can be stored on a CD-ROM. Double-sided DVD-ROMs (DVD-ROMs that store data on both sides), can store up to 26 times the amount of information stored on a CD-ROM.

A DVD+RW is similar to a CD-RW, except it has storage capacities up to 4.7 GB. To write on DVD+RW discs, you must have a DVD writer.

Along with processor speed, amount of memory, and hard disk capacity, CD-ROM drive speed is a featured element of almost every personal computer advertisement. Like CD-ROM drives, DVD-ROM drive speeds are indicated with the letter X to represent the standard speed of a DVD drive. That speed, however, is considerably faster than the data transfer rate of the original CD-ROM. While a 24X CD-ROM drive has a data transfer rate of 3,600 KB per second, a 5X DVD-ROM has a data transfer rate of 6,750 KB per second.

10 | Tape

Magnetic tape was developed in the mid-1950s to replace the earlier method of storing data on punched cards. To better understand the difference between sequential access and direct access (or random access), compare an audio cassette tape to a CD-ROM. An audio cassette tape is sequential; to listen to the fourth song it is necessary to listen to (or fast-forward through) the first three songs. A CD is direct; it is possible to go straight to the fourth song. For what applications would sequential storage be appropriate? For what applications would it be unsuitable? Tape cartridges can be purchased formatted or unformatted. One-quarter-inch wide cartridge tapes typically are 600 feet long. Unattended tape backup is a great time saver. Consider how many 1.44 MB floppy disks are needed and how much time is required (removing disks as they become full and inserting new disks) to back up 150 MB of data. With tape backup, you can press a key, go about other business, and return to remove the finished backup tape.

11 | Enterprise Storage Systems

Large business users often utilize an enterprise storage system strategy. Why? What makes an enterprise storage system strategy attractive to large business users?

12 | PC Cards And Miniature Storage Media

Smart cards can hold the equivalent of 30 typewritten pages of data and cost from $5 to $50. Smart card readers are about $100. As a storage media for an individual’s medical history, smart cards offer obvious benefits. The cards can be carried in a wallet with, or in lieu of, an insurance card, providing both insurance records and an immediate, up-to-date medical history. A form of smart cards, called Personal Information Carriers (PICs) is being adopted by the army to replace dog tags. Think of other ways that smart cards and electronic money (e-money) could be used. Will digital cash someday replace conventional currency? Why or why not?

13 | Microfilm And Microfiche

Microfilm and microfiche images are so small that they can be read only with a microfilm and microfiche reader. Large organizations use microfilm and microfiche to archive inactive files.

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