To USB or Not to USB


USB 3.0 Speeds – Effective Throughput

This quick article is to correct some press impressions that may set expectations to a different level than what is actually planned.  I am a great fan of USB 3.0, so my views are biased.  I just don’t want the critics beating up USB because they expected.

The USB 3.0 Promoters are targeting a 350 Megabytes per second effective throughput for USB 3.0. This is 10x faster than the effective throughput of USB 2.0 (about 32 Megabytes per second). 

The actual signalling rate of USB 3.0 is actually higher, something like 600 Megabytes per second, however, because of the protocol overhead, hardware, device, operating system, and driver latencies, the effective throughput lower.  This is true of all devices you and I own today, not just USB.  It is the reason why USB 2.0 goes at 350 Megabits per second of effective throughput instead of 480 Megabits per second (again the electrical signalling rate).  Of course, the USB 3.0 Promoters are doing everything they can to minimize this.

This is cool because the USB 3.0 Promoters are actually targetting an EFFECTIVE throughput, rather than the more engineering oriented signalling rate.  Also, I think it’s important to set expectations so that when data rates actually meet the expected effective throughput, the critics won’t be saying “you didn’t meet your goals” when really the goals were met.

I think USB 3.0 is going to be fantastic.  I can use the bandwidth.  Yeah, I’m a USB Chauvanist.

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