Universal Serial Bus (USB) has been with us since 1996 and USB 2.0 since 2000. USB 2.0 has been the defacto standard peripheral interconnect for quite some time. Now USB 3.0 is out. Since it’s the newest version of the standard, we might assume that it should be used over the 2.0 standard. It’s true that 3.0 comes with many improvements over the older version. However it also has some drawbacks. Let’s take a look at the major pros and cons of USB 3.0.
You’ll notice from the attached image the enhancements USB 3.0 implements in the connectors. This allows USB 2.0 devices to plug into the USB 3.0 mating connector. However, that does not work in reverse. A USB 3.0 Type B connector will not work with a USB 2.0 Type B receptacle. A USB 3.0 Type A, such as on a thumb drive, will fit in a USB 2.0 receptacle. Obviously you do not get the speed and benefits of 3.0 from a 2.0 receptacle.
In essence, physically, USB 3.0 is USB 2.0 with additional pins, allowing backward compatibility with 2.0 devices.
Faster – Yes, as you would expect USB is faster than USB 2.0. Roughly ten times faster, 625MB/sec vs 60 MB/sec. Depending on your application, this can be significant. In many applications, however, this will simply move the bottle neck to another point in the data transfer chain. The good news is that it is backwards compatible with USB 2.0. Of course to get the higher speed, USB 3.0 supported devices must be on both ends of the cable.
More powerful – One of the unique advantages about USB is that it provides power as well as data. And USB 3.0 provides roughly 80% more power than USB 2.0.
Simultaneous bi-directional transfers – USB 2.0 sends data both directions but only one direction at a time. This is fine if your application shares data one direction at a time. A thumb drive is a typical device that, for the most part, transfers data either to the drive or from the drive but not at the same time. USB 3.0 uses a dual simplex architecture which allows bi-directional transfers. It uses two pairs of data wires instead of one so there is no need to turn the bus around or worry about collisions.
Power consumption – Less power is required to drive the interconnect which means longer battery life or less power draw for systems where power is a premium.
Cost – The most noticeable drawback is the cost. Although the 3.0 standard has officially been out since 2008, it still comes at a higher cost. As a result, many applications that don’t need the improvements of 3.0 continue to implement the 2.0 version. This slows the adoption of 3.0 and results in the cost staying higher. It’s expected that the cost will come down assuming 3.0 becomes ubiquitous as most assume it will.
Cable Length – Another downside to 3.0 over 2.0 is cable length. USB 2.0 support cables of up to sixteen feet in length. USB 3.0 support cables no longer than ten feet. However, you can concatenate up to six cable using five USB hubs. There are also USB extenders for longer runs using CAT5 cabling.
Your Requirements Will Define Your Answer
The good news is that you have USB options for your next system design. For those motherboards that don’t support 3.0, you can use PCIe boards that provide multiple USB 3.0 ports. So consider the requirements of your next system and compare the advantages of USB 2.0 vs 3.0 and select the version that’s right for your application.
CP Technologies provides standard and custom integrated industrial computer systems tailored exactly to customer application requirements and currently offers USB 3.0 support across all their platforms.