SD Speed Class/UHS Speed Class

Greater Performance Choices

There are two kinds of Speed Class, "Speed Class" and "UHS Speed Class."

As a characteristic of flash memory, actual transfer speed varies. Variable speeds are difficult to reliably record streaming content such as video because it requires a constant writing speed. Speed Class and UHS Speed Class provide the constant speed necessary for video recording by designating a minimum writing performance so that minimum and constant speed is guaranteed for camcorders, video recorders and other devices with video recording capabilities under the conditional write operation specified in the standard.

Speed Class, designated as Class 2, 4, 6 and 10, is designed for normal and high speed bus interface (mode) and UHS Speed Class 1 is designed for UHS bus interface*. (Speed Class and the UHS Speed Class are not compatible.)

*UHS (Ultra High Speed), the fastest performance category available today, defines bus-interface speeds up to 312 Megabytes per second for greater device performance in SDXC and SDHC devices.

	Marks	Operable Under...	Applications	SD Memory Card
Speed Class		Normal Bus I/F	SD video recording	SD, miniSD, microSD SDHC, miniSDHC, microSDHC SDXC, microSDXC
			HD ~ Full HD video recording
		High Speed Bus I/F	Full HD video recording HD still consecutive recording
UHS Speed Class		UHS-I Bus I/F	Full higher potential of recording real-time broadcasts and capturing large-size HD videos	SDHC UHS-Iand SDXC UHS-I

UHS Speed Class Compatibility

Speed Class Compatibility

Fragmentation and Speed

The memory of a card is divided into minimum memory units. The device writes data onto memory units where no data is already stored. As available memory becomes divided into smaller units through normal use, this leads to an increase in non-linear, or fragmented storage. The amount of fragmentation can reduce write speeds, so faster SD memory card speeds help compensate for fragmentation.

The SD Association developed standards specifying operating conditions for SDHC, SDXC, SDHC UHS and SDXC UHS memory cards to guarantee the minimum speed according to the card's speed class. Speed logos are provided to help identify cards that comply with these standards.

Lexar starts shipping 64GB, 128GB SDXC cards

Lexar Media has announced that it is now shipping its Lexar Professional Secure Digital Extended Capacity (SDXC) 133x memory card in 64GB ($200) and 128GB ($330) capacities. The latter is an industry first, meaning that you won't find 128GB SDXC cards from anyone else.

With these larger capacities, Lexar Professional 133x SDXC cards are better for shooting continuous, rapid-fire images as well as extended lengths of 1080p HD video. They also offer a Class 10 speed rating with a minimum guaranteed speed of 133x (20MBps), a limited lifetime warranty, and free technical support. This Lexar series also comes with the company's Image Rescue software, which helps recover lost or deleted photo and video files.

"We saw a demand for a professional card that would allow photographers to not only capture more high-resolution images and HD video, but to also take advantage of the full capabilities of their high-performance digital SLRs and camcorders," Pachi Chen-Wong, senior product marketing manager at Lexar Media, said in a statement. "With the new Lexar Professional SDXC cards, we developed a product that will enhance the professional photography workflow. With capacities of 64GB and 128GB, photographers can capture, store and transfer more images and HD video in one place than ever before."