Recent laboratory testing by Multimedia World, a publication which specializes in multimedia technology, revealed that some 4.5X drives actually offer better performance than the 6X drives tested. One reason for the outcome is that many drives do not meet their published performance specifications; another is that the data transfer rate is not as critical as the access time in determining performance.
The traditional basis for comparing drives was selected because it is simple. The original single-speed CD-ROM drives with a 150kbps data transfer rate were improved upon by increasing the data transfer rate in multiples of the initial speed: dual-speed, quad speed, 4.SX, and 6X, with 8X now beginning to appear. Theoretically, the 6X machines should transfer data at 900-kbps and the 4.5X at 675X.
The actual transfer speeds of 6X machines tested, however, ranged from 807 to 922kbps, and the 4.5x machines ranged from 595 to 686kbps. [The higher the number the better.1 More important, the access time in milliseconds ranged from 147 to 229 for 6X drives and 138 to 235 for 4.5X drives. (The lower number the better.] The fastest access time for any drive tested was 138 milliseconds for a 4.5x drive from Plextor (Model 4Plex 43CS Plus at $329]. The second best access time was delivered by a 6X machine. Therefore, it was not possible to conclude that 6X drives are necessarily better than 4.5X drives.
These test results are contained in the following article: Glass, Brett and Don Menn, “Are the Fastest CD-ROM Drives the Best?” Multimedia World, November 1995, pp. 70-80.