Card Speed : SD, SDHC and CF Card

This is an SD, SDHC, CF card transfer speed to MegaBytes per second chart:

Secure Digital (SD)

Secure Digital High Capacity (SDHC)

Compact Flash (CF)

1000x = 150MB/s
 966x = 145MB/s
 933x = 140MB/s
 900x = 135MB/s
 866x = 130MB/s
 833x =  125MB/s
 800x = 120MB/s
 766x = 115MB/s
 733x = 110MB/s
 700x = 105MB/s
 666x = 100MB/s
 633x =  95MB/s
 600x =  90MB/s
 566x =  85MB/s
 533x =  80MB/s
 500x =  75MB/s
 466x =  70MB/s
 433x =  65MB/s
 400x =  60MB/s
 366x =  55MB/s
 333x =  50MB/s
 300x =  45MB/s
 266x =  40MB/s
 233x =  35MB/s
 200x =  30MB/s
 166x =  25MB/s
 150x =  22.5MB/s
 133x =  20MB/s
 100x =  15MB/s
  66x  = 10MB/s (SD speed class 10)
  40x  = 06MB/s (SD speed class 6)
  26x  =  04MB/s (SD speed class 4)
  13x  =  02MB/s (SD speed class 2)

The speed of the card is either specified in “x” transfer speed ratings (300x) or in MB per second (45MB/s). This is based off the system used for the original CDROMs, which is 150 KB/s. For our purposes, this can better be read as 0.15MB/s, since 1,000 kilobytes = 1 Megabyte (150 kB/s = 0.15 MB/s). So:

“x” transfer rate x 0.15MB/s = speed rating in MB/s.

Thus, 300x transfer speed rating would be: 300 * 0.15 MB/s = 45 MB/s

Manufacturers rate the speeds of their cards (not a governing agency), so actual transfer speeds can, and will, vary. Some manufacturers rate speeds by read access, others by write access.

See: http://en.wikipedia.org/wiki/CompactFlash#Speed for more