One of the most common frustrations photographers face is deciphering the different speed ratings for memory cards, hard drives, and data transfer interfaces. With so many numbers, specs, and measurements floating around, it’s easy to feel overwhelmed when trying to optimize your workflow for speed.
The USB 2.0 Bottleneck
A reader recently asked why his photo imports into [Adobe Lightroom](http://www.bhphotovideo.com/c/product/845955-REG/Adobe_65165061_Photoshop_Lightroom_4_Software.html) were so slow. He was using a USB 2.0 card reader and wondered if upgrading to a [newer Mac](http://www.bhphotovideo.com/c/buy/iMac/ci/6490/N/4110474295) with USB 3.0 or Thunderbolt would help. (At the time of writing, Thunderbolt CF/SD card readers aren’t widely available—though there was a [Sonnet Thunderbolt adapter](http://www.bhphotovideo.com/c/product/827757-REG/Sonnet_ECHO_E34_Echo_ExpressCard_34_Thunderbolt_Adapter.html) for pro video users, now discontinued.)
The short answer? USB 2.0 can indeed be a major bottleneck, but a slow memory card can also slow things down. To find the weak link, we need to compare transfer speeds at each stage of the process.
Decoding Speed Measurements
Data transfer rates (like those for USB or Thunderbolt) are usually measured in megabits per second (Mb/s), while memory card and hard drive speeds are listed in megabytes per second (MB/s). Here’s the key conversion:
1 MB/s = 8 Mb/s
This difference in units can make it tricky to compare speeds across devices.
USB 2.0 vs. USB 3.0 vs. Thunderbolt
1. USB 2.0 maxes out at 480 Mb/s (60 MB/s) in theory, but real-world sustained speeds are closer to 280 Mb/s (35 MB/s).
2. USB 3.0 delivers 5 Gb/s (625 MB/s), far exceeding even the fastest memory cards.
3. Thunderbolt (especially Thunderbolt 3) offers even higher bandwidth, but most current memory cards don’t come close to saturating USB 3.0, making Thunderbolt overkill for card readers—for now.
Memory Card Speeds
The fastest CF cards hit around 125 MB/s, while top-tier XQD cards (like [Sony’s XQD S-Series](http://www.bhphotovideo.com/c/search?Ntt=sony+xqd+s+series&N=0&InitialSearch=yes&sts=ma)) reach 168 MB/s—still well below USB 3.0’s limit.
Hard Drive Limitations
Your storage device can also slow things down:
1. Standard spinning hard drives (HDDs) typically run at 60–120 MB/s.
2. SSDs and RAID 0 arrays are much faster but may not be standard for all users.
3. External FireWire 800 drives usually deliver 65–85 MB/s, while USB 3.0 externals (like the [WD My Passport](http://www.photographybay.com/2012/12/03/western-digital-my-passport-edge-usb-3-0-review/)) hit ~115 MB/s.
Testing Your Drive Speeds
1. Mac users: Try the free [Blackmagic Disk Speed Test](https://itunes.apple.com/us/app/blackmagic-disk-speed-test/id425264550).
2. Windows users: Use Device Manager or a tool like [Roadkil’s Disk Speed](http://www.roadkil.net/program.php/P13/Disk%20Speed).
The Bottom Line
For most photographers, a USB 3.0 card reader (like the [SanDisk ImageMate Pro](http://www.bhphotovideo.com/c/product/810152-REG/SanDisk_SDDR_289_A20_ImageMate_All_in_One_USB_3_0.html)) paired with fast cards will eliminate bottlenecks. If you’re using a Mac with an SSD, you’ll have plenty of speed headroom. For external storage, consider a Thunderbolt drive (like [WD’s Thunderbolt Duo](http://www.photographybay.com/2012/04/05/wd-thunderbolt-duo-is-here-and-smokin-fast/)), though they’re pricier.
While Thunderbolt card readers may arrive eventually, USB 3.0 is more than enough for today’s memory cards. By understanding these speed ratings, you can optimize your workflow and avoid frustrating slowdowns.