cd or dvd

Original CD-ROM drives could read data at 150 kibibytes (150 × 210 bytes) per second. As faster drives were released, the write speeds and read speeds for optical discs were multiplied by manufacturers, far exceeding the drive speeds originally released onto the market. In order to market increasing drive speeds, manufacturers used the symbol nX, whereby n is the multiple of the original speed. For example, writing to a CD at 8X will be twice as fast as writing onto a disc at 4X.

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