PC Hardware in a Nutshell, 3rd Edition

CD-ROM Drive Performance

Although CD-ROM drives differ in reliability, the standards they support, and numerous other respects, the most important issue for most users is performance. But performance is not accurately described by the simple transfer rate number that most manufacturers use to characterize drive performance. There are actually two important performance metrics:

Data transfer rate

How fast the drive delivers sequential data to the interface. Data transfer rate (DTR) is determined by drive rotation speed, and is specified as a number followed by an X. All other things equal, a 32X drive delivers data at twice the speed of a 16X drive. But note that we have used 16X SCSI drives that transfer data faster than some 32X ATAPI drives, so it’s a mistake to depend solely on X-rating. The specifications for some drives list only maximum burst transfer rate, which is always the advertised number, while others list sustained transfer rate, which is far more important to overall drive performance. Fast DTR is most important when you use the drive to transfer large files or many sequential smaller files—e.g., for gaming video.

Average access time

How fast the drive accesses random files located anywhere on the CD. Average access time is only loosely tied to DTR, is determined by the quality of the head actuator mechanism, and is rated in milliseconds (ms). Some inexpensive drives have very high nominal DTR ratings but relatively poor average access performance. To make matters ...