The Gadgets Page » Understanding SD flash memory card speeds: "Understanding SD Card Speeds

While the first SD cards were very similar between brands, each brand now offers cards in several different speeds for each capacity. To make things more confusing, SD card speeds are measured in two different ways: in kilobytes or megabytes per second (KB/s or MB/s) and in an “x” rating similar to that of CD-ROMS. The “x” is the minimum CD-ROM speed of 150KB/s, so here’s a table of equivalent speeds:

* 4x: 600 KB/s
* 16x: 2.4 MB/s
* 40x: 6.0 MB/s
* 66x: 10MB/s
* 133x: 20MB/s"

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