SanDisk 16GB SDHC UHS-1 Extreme Class 10 writing at 20MB/s instead of 45MB/s ?

[h4150h4150]

Wonder if anyone here has experience with the Sandisk 16GB SDHC SD UHS-1 Extreme Class 10 card?

I bought one recently and tried it on 2 laptops, both gave read/write speed of about 20MB/s instead of the specs 45MB/s.

Do I have to enable something on the sdcard reader to achieve higher reading speed?

[arthurleung]

Most laptops' card reader is only USB 2.0, 20MB/s is just about right.

I have one of those Sandisk SDHC rated at 45MB/s. Get about 47MB/s out of it with a USB 3.0 card reader.

[Agent]

It's not just a USB 2 thing. Loads of card reader / writers won't be able to hit that speed as they'll use el-cheapo controllers.

[h4150h4150]

Most laptops' card reader is only USB 2.0, 20MB/s is just about right.

I have one of those Sandisk SDHC rated at 45MB/s. Get about 47MB/s out of it with a USB 3.0 card reader.

Thanks for the info, no wonder is it only running at 20mb/s.

I was trying to use it to transfer files between the 2 laptops, both of which only have usb 2.0. I didn't know that the SD card reader is linked to, and thus limited by, the usb 2.0 speed.

Just curious are all, or most, SD card readers tied to the usb controller? I thought they have their own controllers.

[Agent]

The card controller and the interface are 2 separate things.

You'll have a controller that controls the flow of information from the bus (Could be USB right through to serial) to the card, and one that controls the actual interface itself. In this case, USB.

[h4150h4150]

So, does it mean that 20mb/s is the max I could achieve on my sd card reader?

I was thinking if the sd card reader is like the dvd or hdd drive with DMA modes that I can tweak to make it go faster.

[Agent]

So, does it mean that 20mb/s is the max I could achieve on my sd card reader?

I was thinking if the sd card reader is like the dvd or hdd drive with DMA modes that I can tweak to make it go faster.

Yes, you're limited by the hardware. There are no settings you can change to make it faster.

DMA and such things are mostly legacy these days. I can't think of anything that doesn't auto-negotiate to the highest speed possible assuming the BIOS is setup correctly (not having a USB2 port set at 1.1 for example)