An overview of Thunderbolt Technology

We have been spending a lot of time with Thunderbolt on Windows with the ASUS P8Z77-V Premium motherboard, Pegasus R4 and Apple display.

The promise of Thunderbolt connectivity has been around for a couple of years now. Today, Thunderbolt is finally finding its way to the PC platform in the form of motherboards from ASUS and MSI. First unveiled as "Light Peak" at the Intel Developer Forum in 2009, the technology started out as a way to connect multiple devices to a system over a fiber optic cable (hence the 'light' in the name), though the final products have changed the implementation slightly.

The first prototype implementations actually used a USB-style connection and interface. It further required fiber optic cables. When it was renamed to Thunderbolt and then released in conjunction with a new lineup of Apple MacBook laptops, not only did the physical interface move to a mini-DisplayPort connection but the cable was made to use copper rather than fiber. Without diving too far into the reasons and benefits of either direction, the fact is that the copper cables allow for modest power transfer and are much cheaper than fiber optic variants would be.

Thunderbolt's base technology remains the same, however. It is a transfer standard that allows for 10 Gbps of bandwidth for each channel (bi-directional) and concurrently supports both data and display connections. The actual interface for the data path is based on PCI Express and connected devices actually appear to Windows as if they are internally connected to the system which can offer some interesting benefits – and headaches – for hardware developers. The display connection uses the DisplayPort standard and can be used along with the data connection without affecting bandwidth levels or performance.

For current Intel processor implementations, the Thunderbolt connection is supported by a separate controller chip on the motherboard (or a riser card) – and some routing is required for correct usage. The Thunderbolt controller does not actually include a graphics controller, so it must be fed an output from another graphics processor, obviously in this case directly from the Ivy Bridge / Sandy Bridge processors. In theory, these could be from other controllers, but with the ubiquitous nature of integrated processor graphics on IVB and SNB processors, this is going to be the implementation going forward according to motherboard and system designers.

Continue reading our review of Thunderbolt on Windows and the ASUS P8Z77-V Premium!!

The x4 PCIe connection is required for peak performance on the Thunderbolt connection. Therefore, you will see all motherboard vendors implementing it in this way.

We actually started hearing about Thunderbolt / Light Peak before we saw the first USB 3.0 implementations so there was some worry about a battle between the two connection interfaces. Luckily for USB 3.0 it has a significant lead in terms of install base – and user mind share – with nearly all motherboards and notebooks integrating a USB 3.0 controller of some kind. Even Intel's latest 7-series chipset embeds a USB 3.0 controller.

In truth, the connections are different enough that I think both can co-exist without much tension. While Thunderbolt does offer twice the total amount of bandwidth compared to USB 3.0, it is currently targeting solely high-end users that need that much bandwidth. Attaching a single SSD to a USB 3.0 connection can come close to reaching peak utilization but it takes two or more to do so on the Thunderbolt implementations I have tested thus far. For video editors and professional users that want some form of external drive connection without sacrificing speed, Thunderbolt will offer the best option.

Another great advantage of Thunderbolt is its ability to daisy chain across multiple devices on a single connection. You can string several Thunderbolt devices together including external storage, connection hubs and displays as long as the devices correctly implement daisy chain capability – which some of them are confusingly NOT doing. This provides more use for the 10 Gbps of bandwidth provided by Thunderbolt as you could string two RAID arrays that can hit ~ 400 MB/s each and still see the ideal performance from them on your system.

And while there has been a lot of talk about the Apple Thunderbolt display, you can absolutely use any monitor with a DisplayPort connection (or with an active adapter). Keep in mind that it must be the last (or only) devices on the Thunderbolt port.

If you have priced out a Thunderbolt cable at all (currently only available from Apple…) you'll find a $49 price tag in your face. While troubling, there is a reason for this kind of price. Each cable actually has active processing at each end that is able to amplify the channels and information. For these copper-based cables, power transmission is also there for as much as 10 watts so that otherwise passive devices like hard drive docks can operate as expected.

During Computex this year, Intel claimed that other Thunderbolt cable manufacturers were going to be making their way into the market to help drive down these prices sometime in the second half of 2012.

In the near future, purely optical cables will be available and will still use the same mini-DP style connector. It will be backwards compatible with current Thunderbolt implementations.

Even in a daisy chained environment, power can be passed down the chain as long as the devices in between are physically plugged into an outlet. The final, terminating, device cannot pass power.

Because the Thunderbolt data connections are actually just PCI Express interfaces, the Windows device manager will show you some interesting trees of connections when organized by connection rather than type. You can see that as you chain devices together. They will be found further and further down the tree as each Thunderbolt controller (on each device) will become a switch for transferring the signal down and upstream.