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Optical Drive Performance

Optical drive speeds are specified using an "X-factor." The earliest CD-ROM drives transferred data at a constant 150 KB/s, the same rate used by audio CDs, which is referred to as 1X. Later CD drives used variable speeds, changing the speed according to where the head was positioned on the CD. It's impossible to assign a single speed rating to such a drive, so manufacturers began specifying the maximum speed those drives used. For example, a CD-ROM drive that transfers data at a maximum rate 52 times the 150 KB/s audio CD rate, or 7,800 KB/s, is called a 52X Max drive.

DVD drives use the same kind of speed rating scheme, but the DVD "X-factor" is different. The 1X DVD rate is 1.321 MB/s, which is the data rate required to store 60 minutes of video on a 4.7 GB DVD disc, or about nine times faster than a 1X CD-ROM drive. For example, a 16X Max DVD drive transfers data as fast as about 21 MB/s, nearly three times the rate of a 52X CD drive.

To complicate matters further, optical drives do different tasks at different rates. For example, a typical early CD writer could write CD-R (write-once) discs at 4X, or 600 KB/s, but read discs at 24X, or 3,600 KB/s. When CD-RW (rewritable) discs were introduced, yet a third number was needed, because most CD writers wrote CD-R discs and CD-RW discs at different speeds. A typical modern CD writer might read CD discs at 52X, write CD-R discs at 52X, and rewrite CD-RW discs at 32X. Such a drive is referred to as a 52-52-32 drive.

So matters remained, until the first hybrid (or "combo") CD writer and DVD-ROM drive was introduced. At that point, a fourth number was needed to report the DVD-ROM read speed. A typical combo drive might write CD-R discs at 52X, rewrite CD-RW discs at 24X, read CDs at 40X, and read DVDs at 16X. Such a drive is referred to as a 52-24-40-16 drive.

Along came DVD writers, most of which read and write DVD-R, DVD-RW, DVD+R, and DVD+RW, often at different speeds. Most recent DVD writers can also write dual-layer DVD+R/DL and DVD-R/DL discs, also at different speeds. So, the apparently simple question, "Which drive is faster?" often has no simple answer.

Actual read and write speeds also vary from drive to drive, even if the drives have identical speed ratings. In addition to native differences between drives, performance depends on the brand of discs, the firmware version installed, and so on. For example, Drive A, rated to write DVD+R discs at 16X, may write those discs faster than Drive B, which is also rated for 16X DVD+R writes. Conversely, although both drives may be rated for 8X DVD+RW writes, Drive B may write DVD+RW discs faster than Drive A. But if you use a different brand of media or update the firmware in one or both of the drives, the positions may be reversed.

Finally, random access time may matter to you. In general, optical writers have more complex and heavier heads than read-only optical drives. Consequently, optical writers have noticeably slower access times than most read-only drives. For example, the random access time of a fast DVD-ROM drive might be 85 milliseconds, while that of a DVD writer might be twice that. Fast access times don't matter for sequential operations such as burning a disc or watching a DVD video. They do matter when you randomly access data from an optical disc, such as occurs when you play a DVD based game. That's why serious gamers usually have two optical drives in their gaming systems an optical writer for general use and a fast DVD-ROM drive for loading games.

More about Optical Drives

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