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Home > Essays > Optical Storage > 12x CD-RW

Monday, February 18, 2002
PCAV vs. ZCLV Recording Technlogies

1. Introduction

Partial-CAV versus Zone-CLV - Page 1

- Introduction

CD recorder manufacturers seeking to achieve ultra high writing speeds have been constantly developing new techniques, enhancing older ones and applying any sort of tweaking to their drives. Sanyo was the first company that announced a Zone-Constant Linear Velocity (Z-CLV) recorder. The only other manufacturer who has developed a rivaling technology is Yamaha, with Partial Constant Angular Velocity (P-CAV).

As most readers of this review might be aware off, the original CD reading and recording standards called for the laser beam to follow a spiral movement of constant velocity under the track pits (the 1's and 0's). Hence, until recently, all recorders used to record these "pits" using the CLV (Constant Linear Velocity) method.

Things, however, have drastically changed recently. New recording technologies have been introduced: Z-CLV and P-CAV respectively.

CD recording fans are expected to ask: What are them? How can they be compared against each other? Which technology is faster/better? So, let's find out. We start our journey into some of the more esoteric aspects of recording. Follow us :-)

- Zone-CLV writing technology

Zone-CLV (Constant Linear Velocity) is the recording method being in use lately by many End-drive manufacturers in order to achieve a higher recording speed. All previous recorders used CLV (constant linear velocity) as the main recording method. The rotation speed, in the inside, of a disc at 16x recording speed reaches up to 8000rpm! The high rotation causes problems on the recorder's mechanism and produces loud noise. Sanyo pioneered the development of the Zone-CLV recording method trying to overcome the above two problems by making use of the latest available manufacturing technologies. When a recorder utilizes the current implementation of the Z-CLV recording method, the CD surface is divided into exactly 3 zones. In each one of these zones, starting from the inner to the outer parts of the CD, the recording speed varies.

As you can see in the left picture, the recording speed at zone-1 (inner part of the disc) is 16x, it then increases throughout zone-2 (at exactly time t1) at 20x and finally reaches an 24x-recording speed at zone-3 (after time t2).

A very interesting (and important) question then arises: how can the drive change instantaneously its motor speed? How can it adapt the laser-beam power and continue writing without actually destroying the disk? The question is indeed very simple: BURN-Proof!!!

This technology (or some other of its rivaling variants) can be used for executing the necessary synchronization between adjacent zones (Zone-1/Zone-2 and Zone-2/Zone-3 in this case). There is no imperceptible gap between the various Zones, at least this is what Sanyo states. (How about testing this claim? Read on and you will be certainly rewarded…)

- P-CAV writing technology

In contrast to the Z-CLV recording technology, the P-CAV method keeps the disc rotation constant in the inner portion of the disc and then it gradually lets it drop down as the laser beam reaches a certain predefined distance from the center of it.. In this scenario the actual linear writing speed smoothly accelerates outwards, until it reaches a top limit. After this point, the writing speed is kept constant (CLV) until the end of the recording phase, as it was done in the past.

This new recording methodology has been developed by Yamaha and has been implemented in all its latest drive models. It is known that at the outer part of a disc there can be recorded 2.5 as many bits as in the inner part of it. Simple arithmetic states that during CLV recording the speed is consequently reduced 2.5 times in the outer part. Conversely, in Full-CAV mode (under a constant motor rotating speed) recording speed should be 2.5 times faster in the outer part.

In the current Yamaha implementation of the P-CAV method, the rotation speed is kept moderate (5500 rpm) in the inner portion of the disc. Compare this with the Z-CLV method where the disc spins at over 9000rpm in the inner part. This helps towards achieving an improved recording quality in the inner portion of the disc. This is due to the fact that a moderate disc rotation reduces the vibration that usually is the sole responsible for corrupting quality during this recording phase.

Moreover, as the rotation speed is kept low, the life of both the laser diode and the drive's pickup mechanism is expected to be extended. If Yamaha had allowed full-CAV, the recording speed would have easily reached 30x! So expect more speedy drives in the immediate future from this manufacturer.

- P-CAV vs. Z-CLV

The Z-CLV recording method of Sanyo utilizes the existing CLV method combined with linking technology developed (and in this case exclusively used) for buffer underrun protection. The writing of a disc is divided into several zones, and the writing speed is kept constant within each zone. When it shifts up to the next speed level, writing is suspended and then restarted using the buffer underrun protection.

You can easily see that small gaps are silently being introduced during this recording method. Hence some objections are raised by other laser manufacturers.

Specifically, Yamaha claims that the P-CAV technology is ideal for Audio CDs and pre-mastering a disc for mass duplication, since no links are produced. Other manufacturers say that Z-CLV doesn't affect writing quality since the link is kept very small, almost down to zero. Of course a disc without any links , in theory will have better quality than with links, however small these are.

But can this proved in real life?

- Tested drives

Yamaha 2200E firmware 1.0C
Sanyo CRD-BP1500P firmware vHg.35
Acer CRW2010 firmware vH.KF
LiteOn LTR-24102B firmware v5S.04
PleXWriter PX-W2410A firmware v1.00
Ricoh MP7200 firmware v1.30
Ricoh MP9200 firmware v1.00

- Tested Media

Ricoh 74min 24x Serial Number: C301R1XXXXXXXXXXX
ATIP start of lead in: -02:32:09 (sector: -11409)
ATIP start of lead out: 74:12:00 (sector: 333900)
Manufacturer code: 97 27 66 - Ricoh Company Limited (Type: 6)
Disc subtype: Medium Type C, low Beta category (C-)
Target writing power: 4

- Testing lab

Digital Drives

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