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Dearth of host devices leaves UHS-II cards hanging

Posted: 20 May 2014     Print Version  Bookmark and Share

Keywords:SD  memory  UHS-II  Toshiba 

The UHS-II bus interface promising up to 312MB/s HD recording speeds for SD memory cards is catching on, though it will take some time before compatible host devices become available in the market.

Toshiba America Electronic Components (TAEC) launched what it claimed is the first microSD memory card to comply with the UHS-II standard last month. The cards are optimised for uses that require fast write speeds, offering significant performance improvements over their predecessors. For example, the 32GB microSD cards have a maximum read speed of 145MB/s and maximum write speed of 130MB/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. Earlier this year, SanDisk announced its Extreme PRO SDHC/SDXC UHS-II card, which offers up to 250MB/s write speeds for use-cases such as continuous burst mode photo shooting with transfer speeds of up to 280MB/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 2Gbit/s.

Developed by SD Association, the UHS-II interface introduces a new pin layout. Second-row pins are added to support the UHS-II bus signals. The first-row pins are retained for use in normal speed, high speed, and UHS-I bus interface signals. This facilitates compatibility and interoperability with existing non-UHS-II host devices.

UHS-II pin layout

UHS-II SD and microSD cards versus the default speed/high speed/UHS-I cards. Source: SD Association

UHS-I cards, which were specified in SD Version 3.01, can transfer anywhere from 50MB/s to 104MB/s depending on their clock frequency and transfer mode. UHS-II raises the data transfer rate to a theoretical maximum of 312MB/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.

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