Data transfer and memory cards

Monday, 17 October, 2016

James and I were in Norfolk a few weekends back completing data collection for his PhD studies (his blog has at least one post relating to this) and the whole topic of data transfer speeds came back to haunt me. Amongst a number of cameras, we had been shooting with the Nikon D700 using a Sandisk 16Gb Ultra card which has read speeds of 30MB/s. We actually filled the card on day 1 (1000 shots) and need to unload the data off it. I had brought with me my cheap and cheerful Integral CF->USB card reader which works fine. Except it took the best part of 30 minutes to copy the data off the card around <5MB/s. Painfully slow.

When we got back I thought I’d dig back into data transfer speeds again. Remember that the firmware (and hardware) in a digital camera will be able to use cards up to a certain specification. The D700 is at least 64Gb cards up to 90MBs (although it might not be able to utilise the full speed of the card). My Fuji XM1 can take 32Gb cards at 50MBs. Now to achieve these speeds during data transfer to a PC, all parts of the chain need to be quick - card, card reader, USB port, bus and hard disk. In this instance the card reader was the limiting factor as it was plugged into a USB3 port on a new laptop. And just as a reminder, USB3 has a throughout of (depending upon what you read), somewhere above 400MBs (and doubling for USB3.1), whilst USB2 somewhere around 35MBs.

So, one lowcost USB3 card reader later and a new (lowcost!) 50MBs SD card, plugged directly into the USB3 port and read speeds race along. Getting this kind of throughout is both cheap and easy, but its not hard to accidentally put a weak link in that chain and see those rates plummet.