Compact Flash (CF) Card X-Speed Rating is not exact same as SD, SDHC and SDXC Card Speed Class Rating which use minimum writing speed as guideline. CF card is based on value of X which translate into 1X = 150 KiloBytes per second. The X-Speed rating is up to writing speed (no minimum writing speed defined which mean it might be lower writing speed). Example, 10X is equivalent up to 1.5 MB/s writing speed.