SD cards come in all sorts of GB sizes and speeds. Today I thought it a good idea to take a look inside an SD card along with breaking out the speed differences.
To start, the SD media is broken down into “Classes” The Class depicts the speeds at which a device reads and writes.
There are different speed grades available, measured the same as CD-ROMs, in multiples of 150 kB/s (1x = 150 kB/s). Basic cards transfer data up to six times (6x) the data rate of the standard CD-ROM speed (900 kB/s vs. 150 kB/s).
The maximum read speed and maximum write speed may be different. Maximum write speed typically is lower than maximum read speed. Some digital cameras require high-speed cards (write speed) to record video smoothly or capture multiple still photographs in rapid succession. This requires a certain sustained speed, or the video stops recording. For recording, a high maximum speed with a low sustained speed is no better than a low speed card. The 2.0 specification defines speeds up to 200x.
Some manufacturers use the read speed in their X-ratings, while others (Kingston, for example) use write speed.
SD Cards and SDHC Cards have Speed Class Ratings defined by the SD Association. The SD Speed Class Ratings specify the following minimum write speeds based on “the best fragmented state where no memory unit is occupied”:[9]
