Memory vs. Storage

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

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.

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.

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.

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.

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?

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.

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?

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.

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.

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?

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?

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.