No Doubt you know all about USB by now. If not, read our quick introductory article about USB's abilities, limitations, and applications.
A Quick Recap
If you aren't up to speed on USB, here's a quick recap. USB 1.1 came out in 1998, transferring data at a max. 1.5 mbit/s at "low speed" and max. of 12 Mbit/s at "full speed." USB 2.0 was released in 2000 and increased the transfer speeds to a mind-blowing maximum of 480 mbit/s. Since the release, other amendments have been added to USB 2.0 over the years.
Mbit/s, or megabit per second is not the same as megabyte per second. There are 8 bits in a byte. This means that 480 megabits per second transfer speed is equivalent to 60 megabytes per second.
Backwards compatibility and construction
USB 3.0 first of all will be fully compatible (or "backwards compatible") with past versions of USB. The actual physical shape of the USB interface remains unchanged, so you can plug any version of USB into any USB port. Of course if you want to take advantage of new USB 3.0 speeds, your device(s) and cable(s) will have to support USB 3.0. Mixing and matching cables and devices of different USB iterations will not hurt anything.
The USB 3.0 interface itself appears the same as USB 2.0 when you just glance at it, but it in fact includes 5 more pins than the USB 2.0. USB 2.0 has always had 4 pins: 2 for data transfer, one for power, and one for grounding. USB 3.0 introduces 5 new pins that sit in a location that can be accessed by USB 3.0 cables and ports, but can be easily ignored by older USB interfaces when plugged in. With the extra pins, the USB 3.0 cable is noticeably thicker.
Four of the five new pins are dedicated to transferring data up and down stream. This is new for USB, since with USB 2.0 the 2 data transferring lines could only transfer data up or down at any given time. Simultaneous up/down transfer is a huge new improvement for USB 3.0.
Speed: USB 3.0 maximum speed is 4.8 Gbit/s
USB 3.0 increased the USB 2.0 max data rate ten-fold to 4.8 Gbit/s (or 600 mega bytes per second). Looking at this on paper, this is super fast. Imagine being able to transfer your entire library of music of 22.5 Gigs (well, that's mine) in a little less than a minute. I actually transferred all of my music from my mac back to my old mac and it probably took around 15 minutes.
Let's be realistic though
Many critics of USB 3.0 (and USB in general in most cases) point out that these are all theoretical data transfer rate specs. It is true that USB 2.0 has rarely (if ever) reached its 480 mbit/s potential. Many are waiting to see what it really does. The ability to transfer up and down simultaneously makes the 4.8 Gbit/s potential a little more reachable. Although data rates will likely greatly improve, many still doubt we will see 4.8 Gbit speeds.
Another barrier in the way of freely flowing data rates is hard drive read/write speeds. There aren't any traditional hard drives available that can read/write at these speeds, so it would seem that the 4.8 Gbit speed wouldn't work out anyway. Newer solid state drives will definitely benefit greatly, however. Compared to traditional drives that contain a physical spinning disk that can only spin at a finite speed, solid state drives (such as flash drives) don't rely on physical moving parts to work.
Real-time tools to benefit greatly
Firewire, an interface that is losing ground in this seemingly neverending format war, still finds comfortable niches in industries that require real-time transfers without any delay. Industries such as music, video, and other miscellaneous media use firewire 400 and firewire 800 to connect I/O instruments that transfer massive amounts of data in real time. A good example is a mixer interface. No one in their right mind would buy a USB mixer with 16 channels or more. Firewire has always performed the best in this application. USB 3.0 might replace firewire completely for real-time I/O applications.
More Efficient Power... and Just More Power
USB 3.0 has increased its current from 100 miliamps to 900 miliamps meaning you can charge and power bigger devices, and/or more devices at once. Not only is there more power, but it's smarter power. When battery powered devices that aren't being charged are connected to a computer, instead of draining power by the host attempting to find a signal, USB 3.0 uses a signal to announce when data transfer is activated.