How Does a Cd Work?

TABLE OF CONTENTS

Introduction ................................................................................................pg. 2

Factors Creating the Demand For Secondary Storage ............................pg. 2

Why Buy Optical ........................................................................................pg. 3

CD Physical Characteristics.......................................................................pg. 4

How Does a CD Work.................................................................................pg 5

What is a CD-R............................................................................................pg 5

What is CD-RW...........................................................................................pg 5

How Does A CD-RW Work .......................................................................pg. 5

Advantages of CD-RW ..............................................................................pg. 5

DVD.............................................................................................................pg 6

DVD VS. CD...............................................................................................pg 6

Glossary ......................................................................................................pg 7

Questions ....................................................................................................

INTRODUCTION

The use of optical storage continues to grow at an incredible pace. The word optical in the computer industry refers to any storage method which uses a laser to store and retrieve data from media. This term includes such devices as CD-ROM , rewritable optical, WORM, CD-R, and optical jukeboxes or autochangers.

Most of us are familiar with CD-ROM, but other terms such as rewritable optical, WORM, and CD-R, may be foreign. Rewritable optical devices use media that allows data to be written repeatedly, while WORM technology writes data permanently to disk. CD-R , stores information permanently to a compact disc and is read on low-cost CD-ROM drives. These devices are currently sold as single or standalone items.

The continuing development of optical technology has opened up many new avenues and created limitless possibilities. Migration software now allows unused data to be moved from its original location to an optical device where it resides until it is needed. Since the only thing that touches the media is the laser, it is the most durable way to store and archive data. Optical storage solutions are also used in a wide variety of applications such as document timing, records retention, backup systems, and desktop publishing.

FACTORS CREATING THE DEMAND FOR SECONDARY STORAGE

Because of its high capacity, low cost, durability, and random access to large amounts of networked information, secondary storage satisfies an essential need of data intensive organizations. This need for secondary storage arises from a number of factors:

Digital convergence. The move towards graphical user interfaces and the success of operating systems, such as Windows, Windows 95, and Windows NT, have resulted in a significant increase in the average size of a stored document. Industry estimates indicate that the average document size has grown almost tenfold (PC Magazine, 03/10/98, "To Write or Rewrite?")

The information superhighway. The explosive growth of on line services, led by the Internet, has resulted in unprecedented use of such services to reach potentially huge new customer base.

Another consideration for the need of reliable secondary storage is the increasing cost of managing storage on network servers. According to Strategic Research Corporation, as storage requirements explode, organizations are finding that the cost of managing the storage is almost four times the cost of the actual storage due to server downtime, backup procedures, and hard disk failures. Low cost secondary storage alleviates many of these additional expenses because the data is permanent and easily portable in case of hardware failure (prnews: 9/9/99).

WHY BUY OPTICAL?

Some may ask what does recordable CD technology have going for it, and why should you be interested? The answer is that CD's have two things that together make it a compelling choice for your removable storage needs. They include low cost per megabyte and near universal acceptance on Pcs. The price of compact disk recordable drives and media have fallen to previously unimaginably low levels. You can find blank CD-R media for under $2 per disk. A little pricier than their CD-ROM counterparts (typically costing around $550), CD-R media (about $12 per disk), which, over time, can save you money. (See the table below from Disk Trend) CDs are also the only storage technology that is portable across hardware and platforms. Because of this standardization, a CD made on any operating system using any CD recorder can be accessed from any computer using any CD-ROM reader. The standard logical and physical interchange format of CD is especially important for companies wishing to archive information, since it minimizes technology risks from changes in operating systems and hardware in the future. WORM and MO hardware and software are proprietary and, consequently, provide no flexibility or scalability to meet changing customer needs. Random Access is another advantage of CDs. Tape does not allow random access to any file. This means that data is sequentially retrieved, leading to delays of up to several minutes between data access. CDs, on the other hand, are randomly accessible, allowing access to any byte of data within 150 milliseconds. CD's random access makes it highly suited for large storage applications (PC magazine, 03/10/98, "To Write or Rewrite?").