Thunderbolt: Beyond USB and eSATA

Very quietly, there's been a war brewing in computer peripheral interfaces. Backed by Apple and Intel, Thunderbolt may end up surpassing both USB 3.0 and eSATA.

thunderbolt-icon-150x113_0.jpgImage credit: Apple

When I started in computing, we had two main peripheral interface choices: RS-232 serial and Centronics parallel ports. Neither was fast. RS-232, which was the more generally useful of the pair, topped out in early days at 20 kilobits per second (kbps). That was then. This is now.

Today, USB 3.0 can hit 625 MegaBytes per second (MBps) and eSATA can handle up to 300 MBps. Intel's creation and Apple's newest darling interface technology, Thunderbolt can blast data along at 10 Gigabits per second (Gbps).

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That's great news! If, that is, you have a PC and operating system that supports Thunderbolt and peripherals that can work with it. There aren't many of any of these at the moment. Apple and Intel want that to change as fast as possible.

Indeed, one reason why USB 3.0 has so slow off the mark was because Intel still hasn't built in support for it in its motherboards. Thunderbolt, though, is already available on some hardware, and will include this new technology, along with USB 3.0, on its 2012 Ivy Bridge motherboard architecture. In the meantime, Apple is already building Thunderbolt into its latest model MacBook Air, MacBook Pro, iMac, and Mac mini computers.

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So what does Thunderbolt bring to the table? Well, according to Apple, Thunderbolt isn't a replacement for USB 3.0, it's a complement to it. I'm not sure quite what they in mind when they say that, I think it may be more of a sop to USB-users who don't want to replace their hardware than a real plan for the future. Certainly, there's no need whatsoever to connect your keyboard or mouse to your computer with Thunderbolt!

What is Thunderbolt anyway?

Thunderbolt was first known as Light Peak. Intel gave it that name because it was meant to be a purely optical technology. By 2009, Intel realized that people like having peripherals that could be powered by the interface, ala USB, so they added support for a copper wire based system. With this, wired based Thunderbolt could transfer up to ten watts (10W) of power (USB 2.0 and 3.0 can only handle up to five watts).

Thunderbolt can handle both DisplayPort and PCI Express with one port and one cable at the same time
As you can see Thunderbolt can handle both DisplayPort and PCI Express with one port and one cable at the same time. That's a pretty nifty trick!

Thunderbolt can still support optical only connections, but I expect only a handful of devices will ever support that use. That said, Thunderbolt, at heart, remains optically based. If you were to carefully tease apart a Thunderbolt transceiver, you'd find two tiny light Vertical Cavity Surface Emitting Lasers (VCSELs) and two tiny photo detectors. The lasers are the width of two human hairs placed side by side. They can transmit light over each of the two channels using fiber-optic cable 125 microns wide. The photo detectors receive the light from the other end, and circuitry within the Thunderbolt interface converts those to wired electrical signals.

Those two VCSELs and accompanying circuity enable Thunderbolt to send and receive up to 10Gbps at the same time. That's none too shabby!

Once those high-speed signals hit the transceiver, a controller switches the raw data into its two supported data transfer protocols: DisplayPort and PCI Express. That, in turn, means that it won't take peripheral makers of devices such as high-end monitors and external hard drives too long to add Thunderbolt compatibility to their hardware. In addition, since both data protocols can be run over a single Thunderbolt cable, one cable type and port can support almost any device using the interface.

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