UHS-II SD Cards Await Capable Devices

May 16, 2014

TORONTO — The UHS-II bus interface for secure digital (SD) memory cards is gaining traction, but it will take some time for manufacturers to bring products to market that take advantage of the new standard. SD card vendors, meanwhile, have unveiled cards with the UHS-II interface. Last month, Toshiba America Electronic Components (TAEC) debuted what it said is the first microSD memory card to comply with the UHS-II standard, the ultra high speed serial bus interface defined in the SD Memory Card Standard Ver. 4.20.

Available in 32GB and 64GB capacities, Toshiba’s new microSD memory cards are optimized for uses that require fast write speeds, such as high-quality video capture. The cards offer significant performance improvements over their predecessors. For example, the new 32GB microSD cards have a maximum read speed of 145 MB/s and maximum write speed of 130 MB/s, which is an 8x write speed improvement and 2.7x read speed improvement when compared to Toshiba’s current UHS-I equivalent cards.

Toshiba’s UHS-II microSD cards have been preceded by cards in other form factors from a number of vendors, including SanDisk, which earlier this year announced its Extreme PRO SDHC/SDXC UHS-II card, which offers up to 250 MB/s write speeds for use-cases such as continuous burst mode photo shooting with transfer speeds of up to 280 MB/s. Panasonic debuted its UHS-II microP2 series more than a year ago, which is aimed at professional high-end devices with a double-layered UHS-II interface that facilitates transfer speeds of 2.0 Gpbs.

UHS-I cards, which were specified in SD Version 3.01, can transfer anywhere from 50 MB/s to 104 m/s depending on their clock frequency and transfer mode. UHS-II raises the data transfer rate to a theoretical maximum of 312 MB/s using an additional row of pins. The new interface was first announced in early 2011. The additional row of pins pose a challenge: While you can buy a UHS-II card and use it like any other SD card you own because UHS-II is backwards compatible, not many devices can use the additional pins.

Brian Kumagai, director of NAND flash memory products for TAEC, as well as president of the SD Association, which develops and publishes the technical standards for SD card technology, said we can expect to see a proliferation of devices that support cards with UHS-II within the next year. “Because of the new row of pins, it sets the stage for equipment manufacturers to take advantage of this enhanced speed capability.”

Doug Wong, senior member of technical staff for TAEC, said UHS-II is the first introduction of a high-speed serial interface to the SD card, which traditionally had a 4-bit wide parallel interface with its own clock. “It was a legacy holdover interface that has existed for some time,” he said. “All high speed interfaces of the future are serialized – maybe multi-lane serialized.”

While many memory standards and specifications already have a next-generation replacement in the works, Wong said the UHS-II standard will be around for some time, since the interface has more bandwidth available than the NAND it’s connected to. “It has a lot of headroom.”

One of the obvious benefits of a faster interface is that data can transfer back and forth between a card and devices, said Wong. With users moving increasingly larger videos, they don’t want to be waiting hours move a file, but even more important is the write speed required by photo and video cameras.

The technology is available to 128GB or higher, but the focus has been delivering SD cards at a price point the market will support. There also other features that can be added to cards, including WiFi capability, micro payment applications for smartphones, and of course the security features offered by “secure digital” cards. “Very few people have used the features of the secure digital card,” said Wong. “It’s an untapped capability. And there’s so much more personal data than ever before.”