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Thunderbolt rouses quiet PC world

Posted: 10 Mar 2011 ?? ?Print Version ?Bookmark and Share

Keywords:Thunderbolt? MacBook Pro? USB 3.0? Light Peak?

The maturing computer industry has not welcomed any brand-new technology for quite some time. But the dry spell ended recently with the arrival of an Intel invention called Thunderbolt, which debuts in Apple Inc.'s new batch of MacBook Pro notebooks.

The Apple press release that announced the company's use of the new Intel interconnect marked the first public mention of the name, which had not even appeared in the blogs that had been churning with rumors of an electrical version of the optical Light Peak technology. Intel had been demonstrating a Light Peak prototype since September 2009, but the concept remained little more than a curiosity. Then Thunderbolt emerged full-blown in the Apple systems late last month and suddenly became a flashpoint.

Intel followed Apple's February 24 announcement by hosting a conference call later the same day to introduce Thunderbolt. The event was so oversubscribed with callers from around the globe that no one could hear the presenter speaking from a San Francisco conference room.

It took a full dayeons in the Internet erafor the full story to emerge. It was another day or so before word leaked out about the misgivings of a silent majority of big PC, display and hard drive makers not listed among the early adopters of Thunderbolt.

Now that the blinding flash is over, the details are emerging in the sober light of day.

Inside Thunderbolt
The Thunderbolt interconnect supports two 10Gbit/s bidirectional channels on a common transport for 40Gbit/s maximum aggregate throughput.

An Intel Thunderbolt controller enables a common transport layer on which both 4x PCI Express Gen 2 and DisplayPort traffic can ride. The underlying transport has its own protocol encapsulation method as well as unique synchronization and traffic prioritization mechanisms for its 10Gb serial lanes.

Thunderbolt presents to the operative system what looks like native DisplayPort and PCI Express traffic, so no new software is needed.

Intel defines several applications for the interface. According to the company, Thunderbolt can be used to create flexible system designs such as thin notebooks or clients could use it to link to high-end drives, displays and other external devices instead of building them all into one box. Essentially, it provides a PCI Express link outside the box.

The interface will be used to send big files quickly among PCs, cameras and drives, Intel says. It will also be used as a straight DisplayPort link to displays.

Intel has produced two Thunderbolt controllers. One supports a single cable with two bidirectional 10Gbit/s Thunderbolt links and consumes about 1W max. The other supports two cables, presumably for less power-sensitive systems such as desktops.

Thunderbolt controller

Intel is producing a 1-W Thunderbolt controller for single- and dual-cable versions.

Intel is the sole supplier of the controllers and is not commenting on their price, except to say the chips are "competitive with" 10Gbit/s Ethernet controllers in cost per gigabit.

Intel wouldn't say whether it alone owns the intellectual property for Thunderbolt or whether other companies such as Apple own any piece of the IP. It did say the technology is available royalty-free and that it will make case-by-case decisions whether to license the interface for use in SoCs. So far, no one has such a license.

Thunderbolt requires new kinds of active cables. For now, Apple is providing the active copper cable for Thunderbolt; the five-wire assembly uses one wire each for the four 10Gbit/s links (two in and two out) and the fifth for management traffic.

An active optical cable is in development to support lengths of tens of meters. It will be available later this year.

mini DisplayPort connector

Figure 2: The Thunderbolt connector is a modified mini DisplayPort type that plugs into existing DisplayPort ports and can carry PCI Express.

The connector itself is a slightly modified version of the mini DisplayPort connector and plugs into existing DisplayPort devices. It can automatically detect DisplayPort and PCI Express traffic. Intel would not identify any third-party connector and cable makers it might be working with for Thunderbolt support.

Thus far, the chip giant is sharing full technical specs of Thunderbolt only under nondisclosure with partners making Thunderbolt products. It plans to release a developer's kit before July that will include the technical specs, but it does not plan to publish details of the spec online.

The roadmap, too, is unclear. Intel could increase the number of 10Gbit/s lanes or increase the lane speed in the future, but it is not saying what it plans or when.

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