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Plextor 48/24/48A
Review by David R. Hedges on 11.21.2002

Product Provided by: Plextor
Retail Value: $159.00

Introduction
Wow. CD burning technology has come an extremely long way in the past few years. Perhaps you can recall only a few years ago, when you were the coolest guy/gal around, because you had a 2x CD Burner, and you could make a CD in less than 40 minutes! Well, times change; people change, and god knows technologies change.

Since Plextor began its legacy by manufacturing SCSI CD-ROM drives, it has done nothing but provide customers with high quality products from a name they can trust. They have managed not only to keep up with the times, but commonly set the standard for quality and performance in optical storage technology. Now manufacturing three lines of products (SCSI, ATA, and USB), Plextor still delivers innovative and high-quality products to customers world-wide.


Optical Storage Technology Overview
After paying even slight attention to the optical storage market over the past months, an obvious observation is how quickly write speeds have been increasing. A valid question to ask is "why buy a 48x burner, instead of just waiting for a 60x burner?" Simply stated: this isn't going to happen...that's why! CD technology depends on spinning a CD very quickly inside the CD drive (over 10,000 RPM). When drives try to spin a CD too fast, the CD will explode. Since they can't spin a CD any faster than a certain amount (safely), the industry has nearly reached a theoretical maximum speed for optical storage.

Consider for a moment a spinning disc. If you were to place a string down as it rotated once, note the length of the string for one rotation would be significantly smaller towards the middle of the CD than it would near the outer rim of the CD. Or, if you're geometrically minded, consider two circles, one with a radius (r) of 2 CM, and one with a radius of 6 CM. To find the circumference (c) of the circle (or the arc length of one rotation), c=
π2r. So for the inner circle, the area covered in one rotation is about 12.6 CM, and for the outer circle it is about 18.8 CM. Basically, for every one rotation, significantly more data will be written/read towards the outside of the CD.

Because of this characteristic of CDs, two main standards arose for CD burning: Constant Linear Velocity (CLV) and Constant Angular Velocity (CAV).

Constant Linear Velocity (CLV)
This method entails sending data to the CD (through the laser diode) at a constant rate (x packets/second). Consequently, the rotation speed of the CD must be decreased at a linear rate to compensate for increasing circumference sizes of successive rotations. Basically, when the data is being sent at a constant rate to the CD, X packets would fill one rotation at the center, but perhaps 4X packets would fill one rotation at the end of the CD. Since data is being sent at a constant rate, the CD has to rotate 4x slower at the end of the CD.

A variation of this method, Zone Constant Linear Velocity (Z-CLV), involves dividing the CD into segments, and incrementally stepping up the write speed at the beginning of each segment. Each segment then uses the CLV technique of slowing the rotation speed of the CD, and keeping the write speed constant.

Constant Angular Velocity (CAV)
This method for burning CDs takes the reverse approach of CLV. Instead of keeping the burn speed constant, and decreasing the rotation speed, CAV keeps the rotation speed constant, and increases the burn speed. What this means, is near the center of the CD, X packets are written to the CD per second, but near the outside of the CD, perhaps 4X packets are written to the CD per second. More data has to be written to the CD near the outer edge per rotation, but each rotation takes the same time as it did near the center.

A variation of this method is Partial Constant Angular Velocity (P-CAV). This method uses CAV until the maximum write speed is reached, at which point the drive will switch to CLV for the remainder of the disc.


The Plextor 48/24/48A uses P-CAV. The advantages to this are that the drive will reach its maximum write speed more quickly than Z-CLV, and then the drive maintains this speed for the remainder of the disc. P-CAV utilizes portions of CAV and CLV to reach the maximum write speed quickly, and maintain it for the entirety of the disc.

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