Types of Offline Data Storage

Hard drives are considered online data storage. This means that data is readily available at high speed. You do not need to do anything special to access online storage.

online data storage

Holds data that is immediately available and can be quickly accessed, as is the case with hard disks.

offline storage

Holds data that is currently unavailable. You use offline storage to store large amounts of infrequently accessed data or to store computer backups.

compact disc (CD)

A plastic or optical disk that can be read using lasers. All compact discs have a maximum storage capacity of 650MB.

digital videodisc or digital versatile disc (DVD)

Based on the same technology as the CD-ROM, DVDs use a much smaller laser and are able to copy many times more the amount of data. DVDs can hold at least 4.7GB of data and as much as 8.5GB.

Another type of storage is called offline storage. Offline storage means that the data is not readily available without some type of user intervention. Offline storage is useful for transferring data between computers, storing large amounts of data, or providing a means of backup.

Offline storage has become a major market for manufacturers as people take information and devices on the road. The mobile workforce demands that information be readily accessible on desktop computers, laptops, and handheld devices. Many products are available that offer incredible performance, reliability, and capacity. Some common forms of offline storage are floppy disks, compact discs, and tapes.

Recently, removable disks with storage capacities from 40MB to 2GB have revolutionized computing. In addition to removable disks, digital videodisc, or digital versatile disc (DVD), technology is also changing the way computer applications, audio, and high-quality digital video are stored and distributed.

In a networked environment, online data can also mean that the data is available through the network. Offline data can also refer to data that has been downloaded from the network for use on a local computer when it is not connected to the network.

Note 

Near-line storage accessibility is somewhere between online and offline storage. For example, a magneto-optical drive that uses a jukebox to store data is not as readily available as a hard drive but can access data without user intervention.

Distribution Media for Applications

In the not-so-recent past, almost all applications were distributed on floppy disks. Now the most common distribution media is CD. If you don't have a CD player (which you should upgrade to) and you buy an application that comes on a CD, look for a card that enables you to order the application on disk. You can usually do so for a minimal fee.

Note that not all applications have this option. For example, an application with 100,000 pieces of clip art that comes on four CDs would be impractical to distribute on floppy disks.

Floppy Drives

Floppy drives, which use floppy disks, provide a convenient way of transferring small amounts of data from one computer to another. Traditionally floppy disks came in two sizes: 31⁄2-inch format and 51⁄4-inch format.

High-density 31⁄2-inch floppy disks can hold up to 1.44MB of data, and high-density 51⁄4-inch floppy disks can hold up to 720KB of data. For the most part, 51⁄4-inch floppy disks are obsolete. There is also a standard for low-density disks, but these disks are also obsolete.

For transferring small amounts of data, the floppy disk is still an extremely popular option. Floppy disks are inexpensive. The standard is mature, and the media is fault tolerant. Not that anyone recommends it, but some information services (IS) professionals toss them about like Frisbees, without any damage to the disk or data.

High-Capacity Floppy Drives

The 31⁄2-inch floppy drive has a long history that is about to come to an end. New floppy standards outperform the 1.44MB capacity of the floppy drive in every aspect. The Imation SuperDisk LS120 and Sony HiFD both offer larger storage capacities and transfer rates five to eight times faster than regular floppies. The SuperDisk LS120 provides 120MB of storage on a single disk, is inexpensive, and has had great success as a replacement for floppy drives in computers from almost all leading manufacturers. The Sony HiFD supports transfer rates up to 1MBps on a 200MB disk. The key feature of both these drives is that they are backward compatible with 1.44MB floppy disks. Most removable disk drives, such as the Iomega Zip, will not work with floppy disks.

Removable Disk Drives

Ten years ago, removable disk drives were the storage choice of graphic designers. When a graphics designer was ready to send artwork to a printer, the artwork would be placed on a 20MB or 40MB removable disk and sent on its way. The mobility of the original removable drives along with their storage capacity proved to be very valuable. A company could invest in an in-house graphics designer for all its original artwork needs.

Removable disks are now more valuable than ever for many more purposes than just printing. Their storage capacities and the variety of models available have made them attractive to many consumers (in addition to graphics artists).

Zip Drives

The Iomega Zip drive is a low-cost, high-volume removable disk drive solution. The Zip disk is about the same size as a floppy disk and uses a similar magnetically coated Mylar disk, called a cookie, as a floppy. Besides these two similarities, the Zip disk is different from a standard floppy disk. The Zip disk can store 100MB of data and spin its disk 10 times faster than a floppy disk. That translates into more data being written to and read from the Zip disk. Iomega also offers an upgraded version of the Zip at 250MB per disk. The Zip 250 drive does support the older Zip 100 disks.

Large Removable Drives

There are several drive options that support 1- and 2GB disks. These disk drives also support much faster transfer rates than their smaller counterparts such as the Zip and the SuperDisk and are comparable to and sometimes faster than hard drives. The Iomega Jazz is available in 2GB and 1GB drives. The Jazz 2GB drive is backward compatible with the 1GB disks. The Orb is a 2.2GB product by Castlewood that sports similar features.

Note 

If you are in the market for a Zip drive, consider buying a USB drive. USB operates at 10MBps, which takes full advantage of the USB-based Zip 250's transfer rate of 1.2MBps. That can be a significant performance improvement over a parallel Zip drive. The parallel Zip 250 has a maximum transfer rate of 800KBps. That is a nearly 50 percent decrease in performance!

Compact Discs

The compact disc (CD) has become a popular storage media. CDs use an optical drive to read data. This is different from the magnetic media that standard hard disks use. This means that CDs are not susceptible to magnetism as hard drives and floppy disks are.

CDs offer several advantages:

• They can store up to 650MB of data.

• They are inexpensive to reproduce.

• They are lightweight.

• If handled properly, they are durable and can archive data for 10 years or more.

compact disc-recordable (CD-R)

A compact disc that can have data recorded on it once using a laser and can be read many times.

CD-Recordable

Traditionally, CD devices were read-only. Now CD-Recordable (CD-R), or CD read/write devices, have decreased dramatically in price and are increasing in popularity. They are considered Write Once-Read Many (WORM) devices.

CD-Rs are excellent drives for archiving data. Many companies must keep data for three or more years. Maintaining data on the hard drive of a server is impractical, because it can lead to large stores of data that are rarely if ever used. CD-Rs enable companies to write any set of data that they select to the CD and to archive that data for future use.

Writing to a CD requires the use of a strong laser. The laser in a CD-R heats the crystal material in a CD to a temperature between 900 and 1,300 degrees Fahrenheit. The heat causes the crystals to melt, creating a deformity that reflects less light. The less reflective area is called a pit and is interpreted by the computer as a one. A reflective area is called a land and is interpreted by the computer as a zero.

CD-Rewritable (CD-RW)

CD-Rewritable (CD-RW) discs can be written to several times. CD-RW drives are excellent because they will work not only with CD-RW discs (which cost as much as $20), but also with CD-R discs, which are less expensive. If you are considering CD-RW as an option, take into consideration that CD-RW discs are not readable on conventional CD-ROM drives. If you need to use the CD on a CD-ROM drive, you will need to use a CD-R disc.

CD-RW works the same way as CD-R at writing data to disc. Rewrites require that a second laser be used by the CD-RW drive to change the nonreflective areas (the pits) to be reflective. The laser heats the desired area to 400 degrees Fahrenheit. That is just enough heat to loosen the crystals in the disc. As the crystals cool, they assume their original structure, which reflects light.

Digital Videodiscs

Digital videodiscs have long been sought after because of their high storage capacity and diverse usage. Now DVD technology is affordable for home entertainment systems, desktop computers, and laptops.

compact disc-rewritable (CD-RW)

A compact disc that can have data rewritten to it several times using lasers. Lasers record data to the disc like a CD-R, but slightly less powerful lasers are used to erase the data. Even weaker lasers are used to read the data.

DVD's potential is in its data storage. DVDs can store a minimum of 4.7GB to as much as 8.5GB on a double-sided DVD. Coupled with its low cost per disc, DVD is an excellent choice for digital video and audio. Movies recorded onto DVD often include additional sound tracks that will play across sophisticated stereo and surround-sound systems, giving the movie a better-than-theater experience. In addition, the picture quality of DVD can be twice that of VHS tapes. And there is still room for more. Many movies on DVD also come with additional multimedia presentations and interactive games that can be played on a computer with a DVD drive.

DVD Platforms

DVD has many variations. Like CD-ROM technology, DVD is versatile, meeting needs from video media to data archiving. The platforms are as follows:

DVD-ROM (Read-Only Media)  Available as read-only. A typical DVD-ROM holds 4.7GB of data-enough space for a full-length movie.

DVD-Video  A standard designed for the video industry. DVD-Video is read-only, like DVD-ROM, but requires a reader that is compatible with the Content Scrambling System (CSS). CSS is used to prevent people from illegally duplicating the video.

DVD-RAM  A rewritable DVD format that will write as much as 2.6GB of data per side.

Note 

DVD is a sought-after replacement for CD technology, not only because of its storage capacity, but also because DVD drives are backward compatible with CDs. There is no loss in investment for users to migrate to DVD.

Tape Drives

Tape drives use a tape cartridge to store data. Tapes are a popular form of backup, because a single tape can hold huge amounts of data. Backups are critical for any computer, because you value your data. Any computer professional can tell you many horror stories of failed drives with outdated or no backups. The good news is there are people who usually can recover your data. The bad news is this method of data recovery is terribly expensive.

Although tape provides high-capacity storage, it is a slow medium to read from and write to. This is not typically a problem when backing up data, because backups are often scheduled for periods of inactivity. When choosing a tape backup device, you should consider these questions:

• How much storage space do you need?

• What throughput do you need for the backup?

• What is the cost of the tape device and the tapes themselves?

• What backup software is compatible with the drive you select?

• Does your computer operating system have a driver for the tape drive, and is the drive on the operating system's Hardware Compatibility List (a list that specifies what hardware can be used with the software)?

Tape Backup Strategy

Tape backups are only as good as the backup strategy in place. There are several methods of backing up data. The key to the strategies is to be able to recover data quickly and without more than a day's loss. An effective strategy requires the following components:

• Daily tape backups with a full backup at least once a week

• Regular use of a cleaning tape

• Monitoring of backup logs for failed backups

• Replacement of heavily used tapes after six months

• Offsite storage of tapes

In addition, a good backup strategy should cover at least a month's worth of data. This strategy requires at least 19 tapes. Four tapes are used for Monday through Thursday. Three tapes are used for the first, second, and third Friday of the same month. The last tape is used on the fourth Friday of the month. This tape is archived for the year. At the end of a 12-month cycle, you should have a full backup on tape for each month. This ensures that you can restore the data from any month of the past year. In addition, the latest four weeks can be restored.