An Evaluation of Secondary Storage Options for the PC

Jim Forrester
February 16, 1999

As is true with most aspects of the personal computer industry, storage technology continues to offer more for less money. The demand for secondary storage, that which is used for backup or archiving purposes, continues to grow for a number of reasons. One driving force is increased capacity of hard drives, which serve as primary storage devices. As this primary storage capacity continues to grow, secondary storage media must also continue to develop in order to offer convenient backup. Further, application files and user generated data files are larger than ever. Again, secondary storage must be available to backup these large files, as well as offer a convenient means of portability between individual computers.

To meet the demand of increased secondary storage capacity, industry has relied on a number of different technologies. These technologies include magnetic, optical, and a combination of the magnetic and optical technologies. The result is a host of different media with different attributes that fill different needs of users.

Magnetic storage technology utilizes magnetic polarities to represent the zero and one bits of digital data. Typically these media are made of some form of plastic that is coated with a magnetic material. These magnetic particles are divided into microscopic arrays called domains (Anderson, 1999). The storage device is capable of reading by determining the polarity of these domains on the media. The storage device can write by setting the magnetic polarities of the arrays on the media.

Computer tape is one common form of magnetic storage. Computer tape is made of flexible plastic, coated on one side with a ferromagnetic material (TechEncyclopedia, 1999). The first quarter inch tape cartridge (QIC) designed for data storage was released by IBM in 1972, more than ten years before the introduction of the first IBM PC (Mueller, 1996). Tape continues to be an attractive storage media, because of its low cost and large capacity. However, all of the different types of tape drives are sequential access devices (Norton, 1997). Therefore, the tape must scroll from the beginning of the reel to wherever the data is located on the tape (Norton, 1997). This means that while tape is an attractively priced media, it is also a slow media. Tape storage is consequently, very suitable for reading or writing large blocks of information at one time, such as backing up an entire hard drive. However, it is a poor media where random access is required, such as storing individual data files.

As mentioned earlier, tape storage is available in a number of different forms. These forms, or standards, offer different options and features (Rigney, 1998). The Travan and DAT forms are currently the industry leaders. The Travan standard was developed by Imation (www.imation.com). Travan is essentially an extension of the QIC tape standard (Rigney, 1998), using a longer wider tape than its predecessors in the QIC standard (www.imation.com/products/data/content/0,1011,1117,00.html). With compression, a single Travan TR4 cartridge can hold up to 8GB (Rigney, 1998). The 8GB tape cartridge can be purchased for $23.95(www.zdnet.com/computershopper ), which translates to $3.00 per GB of storage space. Adding a Travan tape backup unit to a Gateway PC will add $249 (www.gateway.com), while an external SCSI drive will cost about $335 (www.zdnet.com/computershopper ). The Travan form is backward compatible, able to read non Travan QIC tapes.

While the 8GB capacity of the TR4 may seem sufficient to many PC users, hard drive capacities increase every year. Today, hard drives are available with capacities greater than two times the 8GB TR4 standard. Therefore, users wishing to perform a complete backup of data from these larger hard drives may require the digital audio tape (DAT) standard, with capacities greater than 20GB (Rigney, 1998). The newest DAT specification, DDS-3, allows for storage of 12GB of uncompressed data, and 24GB of compressed data (Rigney, 1998). This capacity is achieved using what is called helical scan technology. Rather than writing data to the tape in a parallel fashion as the tape passes across the read/write head, the data is recorded as strips at an angle across the width of the tape (Mueller, 1996 ). While the DAT drives offer substantially more storage capacity, they cost more. A SONY DDS-3 external drive with a SCSI interface is $759 (www.zdnet.com/computershopper ). However, a Hewlett Packard 24GB catridge costs only $19, yielding a cost of just $0.79 per GB of storage; considerable savings over theTR4 cost (www.pricewatch.com ).

Superfloppy disks are another class of data storage media that makes use of magnetic recording technology. Although the standard 1.44MB floppy disk continues to be a popular form of magnetic storage media, demands for larger capacity are pushing this form toward obsolescence. Files downloaded from the Internet and most application files can easily use up more capacity than the 1.44MB offered on a floppy disc. Therefore, needs to move these files quickly and easily to other computers, or simply back up these files requires more than the standard floppy has to offer. The new superfloppies, such as the ZIP and the LS120, with random access storage capacities in the range of 100MB to 250MB, are filling this niche (Windows Magazine, 1998). These are essentially floppy disks, with specific enhancements that allow them to store greater than one hundred times as much as the traditional high-density 3.5 inch floppy disk. The disk, also called a cookie, is made of semi-rigid plastic coated with a magnetic material. The magnetic domains are arranged in concentric circles on the disk.

The Zip Disk superfloppy from Iomega uses standard magnetic recording technology, with an added twist. The twist is the incorporation of the Bernoulli aerodynamic principal in the design of the Zip drive. The read/write head is pulled toward the disk and held in place, just off of the surface of the disk, by air pressure created by the 3000rpm spinning of the disk. The disk can rotate at much higher speeds without causing excessive where on the disk, because the head is not touching. This translates into higher capacity and performance, allowing a Zip drive, which fits in a 3.5" floppy bay of the PC, store 100MB of data in a disk of almost the same dimensions as the 1.44MB floppy. In addition, the Zip has a high market penetration (www.zdnet.com/computershopper /edit/howtobuy/C0000046/size1.html ). This is an important consideration for inter-PC compatibility, allowing easy portability of files. Adding an internal Zip drive to a Gateway PC costs $99 (www.Gateway.com ), while an external parallel or SCSI interface Zip drive can be purchased from Comtech for $89 (www.zdnet.com/computershopper ). A single 100MB ZIP cartridge can be purchased online for $7.99 (www.zdnet.com /computershopper ), or $79.90 per GB of storage. The downside of the Zip disk is that it is not backward compatible, in that it can not read or write the 1.44MB 3.5" floppy disks.

Another option in the superfloppy category is the floptical disk. The floptical is composed of the same materials common to hard disks and floppys. (Mueller, 1996) Optical technology in the form of a laser is used to precisely position the read/write heads. The precise positioning achieved by the incorporation of laser allows for compaction of the magnetic domains, increasing disk capacity 100X. Imation’s LS120 SuperDisk, with a storage capacity of 120MB, is the common floptical drive available today. One attractive attribute of the LS 120 is that it is backward compatible, reading and writing to the standard 720KB and 1.44MB floppy disks (www.superdisk.com/sc/superdisktechfaq.html). The LS 120 can also serve as the PC’s bootable A: drive (Mueller, 1996). An external parallel interface SuperDisk drive costs $149.99 from buycomp.com (www.zdnet.com/computershopper ), while an internal drive is available from Gateway for $69 (www.gateway.com ). A 120MB SuperDisk bought in a ten pack costs $6.59 (www.zdnet.com/computershopper ). This is a cost of $54.92 per GB of storage.

Currently, the last option in the magnetic technology category is removable hard disks. In this case, the disk or platter is very rigid, allowing even more compaction of the magnetic domains that are used to represent data. Leaders in this market are the Iomega Jaz drive and the SYQUEST SyJet. A SCSI external 1.0GB Jaz can be purchased for $199.95 (www.zdnet.com/computershopper), the corresponding 1.0GB cartridge costs $74.00. This provides storage at a cost of $74/GB. The SCSI external 1.5GB SyJet costs $299.99, while its 1.5GB cartridge costs $149.99 (www.syquest.com/ products /sycart.html). This is storage of 1GB at $99.99.

Optical storage is a different technology that provides a growing option for long term back up of data storage. Optical disk media include compact disc technology such as, CD read only memory (CDROM), CD recordable (CDR), and CD read write (CDRW). The newer DVD media also use optical storage technology. The underlying idea of optical technology is that a reflective metallic surface on a disk can be stamped with indentations called pits. Pits may also be burned onto the surface with a laser. These pits alter light reflection when a laser is focused on the metallic surface. A light detection mechanism can determine if the laser has passed over a pit by the altered light reflection. Optical media offer random access. In addition they provide a shelf life of 30 years or greater (Kempster and Geddings, 1998). They are also highly reliable because the laser reads from the disc without physical contact. This prevents wear or breakdown of the disc.

A compact disc has a maximum storage capacity of 650MB (Mueller, 1996). In the case of CDROM, the media can not be altered after manufacture. This means that CDROM is suitable for distributing and backup of software applications, yet it is not a suitable media for data backup. Another form of compact disc, the CDR, can be altered to store data. In this case the CDR drive contains a laser that can alter the metallic reflective surface of the disc, one time. In the case of the CD read write disc (CDRW), the disc can be altered to create a pit with one laser in the drive, while another laser can me used to remove the pit (Kempster and Geddings, 1998). This allows both recording and erasing capabilities. A 650MB CDR disk costs $1.2 and a 650MB CDRW disk costs $3 (www.pricewatch.com ). This translates to $1.85/GB and $4.62/GB respectively. A DVDROM with a CDRW adds $305 to a Gateway2000 PC (www.Gateway.com ).

In addition to the compact disc technology, optical technology includes Digital Versatile Disc (DVD). DVD is a pair of high density CDs back to back (Norton, p. 254). DVD employs the same technical strategy as CD. However, the pits are much closer and the tracks much narrower, allowing for substantially more capacity. A single DVD can be used to store up to 4.7GB(Norton, 1997), more than seven times as much data as can be stored on a CD. DVD is also approximately 9X as fast as a CDROM drive (Mueller, 1996). It is probable that this combination of speed and capacity will help DVD replace CD as the preferred optical storage technology, once recordable and recordable rewriteable DVD technology becomes available. This may be further encouraged by the backward capability of the optical media. Table 1 illustrates the success of backward capability in CD/DVD storage media.

Table 1. Illustrates the success of backward compatibility in the CD/DVD storage media. (Taken from http://www.pctechguide.com/16storage.htm)

The third class of technology, magneto optical (MO), is a hybrid, utilizing both technologies previously discussed. In this case, the media is also a disk containing a magnetic layer. However, the polarity of the magnetic material can not be changed easily, as opposed to the magnetic materials used in other floppy disks. In order to switch the polarity of a region on the disk, the region must first be heated to 392 degrees Fahrenheit with a laser (Glossbrenner, 1997). Raising the temperature changes the magnetic properties on the disk, allowing a magnet in the read/write head to switch polarity. Reading from the MO disk takes advantage of the fact that the magnetic field on the disc can twist a beam of laser light (Glossbrenner, 1997). Detection of the twisted light is used to read data, much like the change of reflection caused by pits in CD or DVD technology. ( See figure 1.) Because the polarity of the magnetic material is not easily changed, MO is more stable for long term storage than other magnetic disks. MO disks offer a rated life of 30 years and can be written to and read from an unlimited number of times (Glossbrenner, 1997). An internal MO drive is not available from Gateway2000. A Maxoptix 5.2GB internal SCSI MO drive is available from Dirt Cheap Drives (www.zdnet.com /computershopper ) for $1499. A HP 5.25", 5.2GB disk costs $76; $14.47/GB of storage (www.pricewatch.com ). The Fujitsu DYNAMO 640MB external SCSI drive costs $406. A Sony 640MB disk is $21; $32.82/GB of storage (www.pricewatch.com ).

Figure 1. Taken from (www.pctechguide.com/images/16kerr.gif)

A number of different storage devices have evolved for the PC, using magnetic, optical and magneto optical technology. These devices fill a number of different functions and needs, addressing factors such as capacity, compatibility, cost and performance (Wells, 1998). Capacity of media today spans the range of 1.44MB to 24GB. Cost of storage can be as cheap as $0.79/GB for sequential access tape, or 100X as expensive at $79.90/GB for a random access SCSI Zip superfloppy. The optical technology are highly backward compatible; whereas the Zip backward compatible with the current standard 1.44MB floppy. Further, the Zip is not compatible with other superfloppies, yet it offers the benefits of high market penetration. Clearly, development of storage technology has provided us with a large number of data storage options for the PC.

Works Cited

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Glossbrenner, Emily and Alfred. (1997). The Computer Sourcebook. New York: Random House.

How to Buy Removable Storage. Windows Magazine Online, [Online]. (1998). Available: http://www.techweb.com/se/directlink.cgi?WIN19980101S0120 [2/8/99].

Kempster, Linda and Geddings, John. (1998). Optical Disc Storage and Retrieval, [Online]. Faulkner Information Services. Available: https://www.rit.edu:8080/_proxy_/www.faulkner.com/products/faccts/00005785.htm.

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