High Speed SD Cards Everything you should know about UHS Bus interface

“Sandisk UHS-II SDHC cards” by Evan-Amos from Wikimedia Commons licensed under Public Domain {{PD-self}}

You  may have heard that recently  sandisk launched their new set of high speed SD cards named as Sandisk Extreme Pro. These cards have memory capacity upto  512 GB, So now you can have as much  memory capacity as your PC’s SSD  in your small and  compact mobile devices such as your DSLR camera. These SD cards are engineered with UHS -I (Ultra high speed) Bus interface. Although these are not the first SD cards manufactured with UHS-I bus interface, though there are very few people who have  relevant  Knowledge about the UHS technology.

So Here is everything you should know about UHS  Technology.

UHS-I BUS Architecture

As you all know that UHS stands for ULTRA HIGH SPEED bus interface and it is very obvious from the name that it supports very high speed data transfer. As according to SD association it is a new standard for high speed bus interface for SD (Secure digital) memory cards specs version 3.01 which supports speed as high as 104MB/s,yes you read it right 104MB/s, its great for a mobile device to transfer data at such a high speed.

Do you want to know how such a high speed is obtained, well here is a quick explanation.

The clock frequency for UHS-I is about 208Mhz, the bus is designed in such a way that it transfer 4 bits for each rise in clock and another 4 bits is transferred when clock falls, hence an entire byte is transferred in just one Full clock cycle. This results in very high speed data transfer upto 104MB/s.

Sandisk Extreme Pro  cards have maximum write speed of 90MB/s and read speed of 95MB/s, Remember when i say 104MB/s it’s a bus interface speed of UHS-I and actual write speed of SD card may be different. The write speed with non UHS-I host devices is just 23MB/s. So you better have a UHS-I compatible device to enjoy those fancy write speed, it is also clear that these SD cards are backward compatible  i.e can be used with older devices having no UHS compatibility with reduced speed. 

These SD cards are perfect for 4K video recording where high write speed is essential. There are many DSLR cameras out there with UHS-I compatibility through which you can record decent looking 4K videos to your Extreme Pro SD card for your HD tv’s. 

UHS-II BUS Architecture

It is no different than UHS-I, the only difference is that it employes an additional row of pins to provide even higher bandwidth than UHS-I. SDHC or SDXC cards employing UHS-II have maximum bus interface speed of 312MB/s. The cards employing UHS-II are also backward compatible and can be used with UHS-I compatible device with reduced speed and can even be used with non UHS compatible devices. There are many  SD card out there which support UHS-II with write speed upto 200MB/s then what makes Sandisk Extreme Pro unique, obviously its capacity. You can record 4k video upto 3 hours with the maximum 128 GB UHS-II SD card where as Sandisk is giving you whole 11 hours of 4K video with its 512 GB.

Its not a long time ago when just 4GB of memory feels enough. Its great to see how technology is changing our world, everyday there is someone with new ideas with new innovations. You must have heard this quote “Necessity is the mother of invention” well sometimes i feel it should be “Imagination is the mother of invention“.


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