Monday, February 1, 2010

Linux and USB 3.0

The newest, fast interface, USB 3.0, is finally out, but only one operating system has native support for it: Linux.

Ever get tired of Windows people proclaiming how their operating system has device support for this, that, and the other thing and Linux doesn't? Well, now you have a perfect come-back.

The newest, fast interface, USB 3.0 is out and only Linux has native support for it.

Linux started supporting USB 3.0 in the September 2009 release of the 2.6.31 Linux kernel. Neither Windows 7 nor Snow Leopard currently supports USB 3.

Windows support? That will have to wait for Windows 7 SP1 ---whenever that shows up.

Long before then, many USB 3.0 devices will have arrived. Some will doubtlessly have Windows drivers, but only Linux is USB 3.0 ready.

USB 3.0, aka SuperSpeed USB, reaches new highs in PC peripheral speeds. USB 2.0 has a maximum throughput of 480Mbps (Megabits per second), which is fast --- but these days, when you might want to move gigabytes of movies from one your PC to an external hard drive, it's not fast enough.

USB 3.0, by comparison, has a maximum throughput of 5 Gbps (Gigabits per second). Of course, that's a peak speed.

In real life, USB 2.0 has an effective throughput of about 32MBps (Megabytes per second) while USB 3 easily laps it at an effective throughput rate of 350MBps (Megabytes per second).

What About Firewire?
Users who have been around for a while may be saying what about Firewire, aka the IEEE 1394 interface standard.

It's true that Firewire, Apple's name for their implementation for the technology, was faster than USB 2.0.

Firewire 400 could reach a peak throughput of 400Mbps and 800 could, as you might have guessed, hit 800Mbps.

Unfortunately, Firewire has never caught on. It was included in some Macs and iPods, but recently Apple has started dropping it from their devices.

While the interface was popular on some higher-end digital video equipment, it seems to be losing ground there as well. And, on PCs, IEEE 1394 ports still appear, but more and more computers are coming on without them.

Linux has long supported IEEE 1394. Recently, in the 2.6.33 Linux kernel, though, Linux has adopted a new and improved Firewire stack.

Be that as it may, the sad truth is that IEEE 1394 has been slowly dying in the marketplace for years and the rise of USB 3.0 will only hasten its departure.

For example, at USB 3.0 speeds, an external drive might very well be faster than the SATA (serial advanced technology attachment) 2.0 hard drive you are probably using in your PC.

At these throughput rates, though, it's the speed of the mechanical drive that's the limiting factor, not the interface.

That said, high-end solid state drives, which can reach over 200MBps throughput, are capable of taking advantage of USB 3.0's speeds.

USB 3.0 manages to achieve its speeds without sacrificing backwards compatibility. It does this by keeping the same basic physical format as the earlier USB cables and ports.

Unlike USB 2.0, which has only four data-carrying wires, USB 3.0 uses nine. With these it supports four-different transfer speeds: low-speed, 1.5 Mbps; full-speed, 12 Mbps, high-speed, 480 Mbps; and 'SuperSpeed,' 5Gbps.

When you attach a USB 3.0 device to a USB 2.0 or earlier port, the devices use a polling mechanism to determine which is the highest supported speed. Once established, the connection proceeds at the established speed.

This also means that USB 2.0 cables aren't engineered to handle connections between USB 3.0 devices.

In short, you'll need to get new cables. You may also notice that the maximum USB 3.0 cable length is shorter than very long USB 2.0 cables.

USB 3.0 can only deliver its full throughput at 3 meters or less instead of USB 2.0's 5 meters.

So you should check into USB 3? I think so. The first laptops are starting to ship with USB 3.0 on board and dozens of devices, mostly external hard drives are starting to arrive as well.

Within a few months, USB 3.0 will be omnipresent in both new computers and devices, and Linux will be the only operating system that comes ready-made to support them.

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