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     This story was printed from CdrInfo.com,

     located at http://www.cdrinfo.com.

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As Arrowkey says "...How fast is that writer? TimeWrite checks actual vs. advertised writer speed! Advertised vs. actual speed differences with CD readers occur. One device claimed to read at 72x, when actual testing showed it read much slower than that speed. Similarly, many users are surprised when their 52x reader does not actually read at 52x over the entire surface of the disc. The same issue is occurring with CD and DVD writers..."

And continues "...CD and DVD writers are rated and compared using the “x” factor which measures their speed in writing to a disc. This factor is based on one “x” being the speed at which an audio CD is played for CD devices, with a similar but faster data transfer rate for DVD devices. Unfortunately for the buyer, this is not a particularly useful measurement, nor is it an indication of how fast the device actually is.

CD devices have three basic techniques of spinning the disc.

CLV: This is the original technique for accessing CD discs and stands for Constant Linear Velocity. This varies the rotation of the disc so that the laser is moving over the disc surface at the same linear speed at the inside and the outside. Since the outside part of the disc is “longer” than the inner part, the disc is spun slower when accessing the outer part than at the inside part.

CAV: In the past few years CAV (Constant Angular Velocity) devices have been introduced where the disc is spun at a constant speed. Most recent devices use this for reading and some variation for writing.

Partial CAV (P-CAV) or Zoned CAV: These are variations where the rotation of the disc changes in relation to the position of the laser but less so than the original full CLV technique. The speed changes in a stepwise fashion rather than continuously over the surface of the disc.

Recently, Jörgen Städje tested and documented that spinning a CD-ROM so that the inner part is accessed at 52x (approximately 27,500 RPM) poses a safety hazard. In that study, Städje found that most discs fragment into thousands of pieces when spun at that speed. According to Städje, if a drive that advertises a 52x speed actually did perform at 52x over the entire disc surface, the disc would shatter.

With CD writers having claimed speeds from 40x to 52x, we are seeing similar issues arising. Yes, a writer advertised as 52x really does only write at 52x near the outer edge of the disc. But, there are other important considerations as well.

There are two different modes that are used for writing to CDs and DVDs:

Continuous mode is used by “mastering” programs and goes by a number of terms like “Disc at Once”, “Track at Once, ” etc.

Incremental writing is used with packet writing and is exclusively used for technologies like DVD+RW and Mount Rainier.

Today, CD writer manufacturer’s speed rating is based only on the writer’s performance in continuous mode. DVD writers differ slightly in that DVD+RW only supports incremental writing, but DVD+RW writing speeds are not advertised as heavily as those for CD writing.

So, how fast does your writer write packets? This may not be important if you’re writing audio discs. Music CDs are written exclusively in continuous mode. However, when using programs like DirectCD, InCD, DLA, or AccuBurn-R, the packet writing speed is important; perhaps more so than the continuous writing speed.

With our AccuBurn-R software, many users have reported significantly different timings when writing discs. They question why AccuBurn-R doesn’t write at 40x when they have a 40x CD writer. The simple answer is the 40x CD writer isn’t writing at 40x all of the time, and may not write packets at anywhere near 40x. A more complete answer requires testing the specific writer.

The question regarding the speed of a CD device can be partially answered by using freeware programs. These programs test the read performance of a drive only, and not the write performance in an accurate manner. They also do not test anything except “continuous” mode writing.

Arrowkey is offering the free TimeWrite program to assist our customers and optical media users in general interested in the “real” performance of their CD writer. This program tests your CD writer in three different modes: variable packet writing, fixed packet writing and track-at-once continuous writing. Included is an “upload” capability allowing you to send your testing results to Arrowkey. These results will be posted on our web server anonymously to be shared with other users. We encourage everyone to post their results of each of the three tests so that your writer can be compared to others.

After we have received results, a future article will appear in the Arrowkey newsletter describing the overall results from this and summarizing the best and worst writer performance that has been reported..."

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