RECORDING SPEED

How long does it take to write a CD-R or CD-RW disc?
The amount of time taken to write a disc depends upon the speed of the recorder, the writing method used by the recorder and the amount of information required to be written. Recording speed is measured the same as the reading speed of ordinary CD-ROM drives and players. At single speed (1x) a recorder writes 150 KB (153,600 bytes) of data (CD-ROM Mode 1) per second and at a multiple of that figure at each speed increment above 1x.

CD Read and Write Average Data Transfer Rates
(transfer rates indicated in bytes)

Writing Modes
As the market for CD-R and CD-RW products came into its own writing speed accelerated due to rapid advances made in hardware and media technology. One breakthrough came in writing modes which permitted recorders to reliably operate beyond 20x speed. Available units now employ a variety of writing modes including Constant Linear Velocity (CLV), Zone Constant Linear Velocity (ZCLV), Partial Constant Angular Velocity (PCAV) and Constant Angular Velocity (CAV).

Constant Linear Velocity (CLV)
CDs were originally designed for consumer audio applications and initially operated using a CLV mode to maintain a constant data transfer rate across the entire disc. The CLV mode sets the disc’s rotation at 500 RPM decreasing to 200 RPM (1x CLV) as the optical head of the player or recorder reads or writes from the inner to outer diameter. Since the entire disc is written at a uniform transfer rate it takes, for example, roughly 76 minutes to complete a full 74 minute/650 MB disc at 1x CLV. As recording speed increases the transfer rate increases correspondingly so that at 8x CLV writing an entire disc takes 9 minutes and at 16x 5 minutes. Recording time as well is directly related to the amount of information to be written so partial discs are completed in proportionally less time. But writing at higher speeds requires rotating the disc faster and faster (eg. 10,000 to 4,000 RPM at 20x CLV which places escalating physical demands upon both media and hardware. Manufacturers have met this challenge by moving beyond the original CLV mode to obtain even higher performance.

Zone Constant Linear Velocity (ZCLV)
In contrast to CLV which maintains a constant data transfer rate throughout the recording process, ZCLV divides the disc into regions or zones and employs progressively faster CLV writing speeds in each. For example, a 40x ZCLV recorder might write the first 10 minutes of the disc at 20x CLV, the next 15 minutes at 24x CLV, the following 30 minutes at 32x CLV and the remainder at 40x CLV speed.

Partial Constant Angular Velocity (PCAV)
Some recorders make use of the PCAV mode which spins the disc at a lower fixed RPM when the optical head is writing near the inner diameter but then shifts to CLV part way further out on the disc. As a result, the data transfer rate progressively increases until a predetermined point is reached and thereafter remains constant. For example, a 24x PCAV recorder might accelerate from 18x to 24x speed over the first 14 minutes of the disc then maintain 24x CLV writing for the remainder of the disc.

Constant Angular Velocity (CAV)
The CAV mode spins the disc at a constant RPM throughout the entire writing process. Consequently, the data transfer rate continuously increases as the optical head writes from the inner to outer diameter of the disc. For example, a 48x CAV recorder might begin writing at 22x at the inner diameter of the disc accelerating to 48x by the outer diameter of the disc.

What is the difference between low and high speed CD-RW discs?
CD-RW media present additional problems in that it is not possible for one kind of CD-RW disc to support all recording speeds. Low speed discs are compatible with all CD-RW recorders and can only be written from 1x to 4x speeds. High speed discs, on the other hand, can be written from 4x to 10x but only on recorders bearing the high speed CD-RW logo.

Can CD-R and CD-RW discs written at different speeds be read back at any speed?
The speed at which a disc is written has nothing to do with the speed at which it can be read back in a recorder, CD-ROM or DVD-ROM drive.

Do some CD-R recording speeds produce better results than others?
Recorder and media manufacturers carefully tune their products to operate with each other across a wide range of speeds. As a result, equally high quality CDs are created when recording at almost all speeds. However, 1x presents a minor exception. Generally speaking, the physics and chemistry involved in the CD recording process seem to produce more consistent and readable marks in CD-R discs at 2x and greater speeds.

Can any CD-R disc be recorded at any speed?
In order to accommodate progressively higher recording speeds CD-R disc design and manufacturing has continued to evolve. Consequently, reliable operation is best achieved by following disc manufacturers’ guidance with respect to the range of writing speeds formally supported by their respective discs, while acknowledging that this can change as recording specifications change. Additionally, new media companies and products continually enter the market and some recorder companies may test particular brands of discs more extensively than others. Thus it may be advisable to inquire of the recorder manufacturer for specific media recommendations.

Is there any way to prevent a recorder from writing a CD-R disc at too high a speed?
CD writing speed can be set at an appropriate level manually in all premastering software to correspond with the recommendations of the recorder and disc manufacturers. Beyond this, some of the latest recorders also employ systems to actively monitor the writing process and automatically adjust recording speed in order to achieve the optimum

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