Fujifilm's new xD-Picture Card is the ultimate solution for the exciting new generation of Digital Camera Review by Gene Wrights. xD-Picture Card is the smallest, lightest flash memory card available today, yet it offers the fast read/write speed and high capacity that today's newest products require.
There are different speeds of SD card available. The official unit of measurement is the Speed Class Rating; an older unit of measurement is the × rating.
The Speed Class Rating is the official unit of speed measurement for SD Cards, defined by the SD Association. It is equal to 8 Mbit/s, and it measures the minimum write speeds based on "the best fragmented state where no memory unit is occupied
The following are the ratings of some currently available cards:
Even though the class ratings are defined by a governing body, like × speed ratings, class speed ratings are quoted by the manufacturers but unverified by any independent evaluation process.
Important differences between the Speed Class and the traditional CD-ROM drive speed measurement ("×" speed ratings) are:
On 21 May 2009, Panasonic announced new class 10 SDHC cards, claiming that this new class is "part of SD Card Specification Ver.3.0". Toshiba also announced cards based on the new 3.0 spec As of December 2009, the SD Association's Web site does not include information on this new class or new specification.
The × rating is a unit of measurement equal to 1.2 Mbit/s. It is derived from the standard CD-ROM drive speed of 1.2 Mbit/s. Basic cards transfer data up to six times (6×) the data rate of the standard CD-ROM speed (7.2 Mbit/s vs 1.2 Mbit/s). The 2.0 specification defines speeds up to 200×, but unlike the class rating system, does not mandate that x-ratings measure the card's sustained write-speed. For most cards, the maximum read speed is typical faster than its maximum write speed, leading some manufacturers to use read-speed as the ×-rating measurement. Other vendors, such as (Kingston, use write-speed.[
This table lists common ratings and minimum transfer rates.