What you need to know about Thunderbolt

The arrival of Apple’s latest MacBook Pro models brings with it a brand-new connection technology called Thunderbolt. And by brand-new, we mean “just announced Thursday morning,” which raises lots of questions about what, exactly, Thunderbolt is and why Apple has chosen to make it a flagship feature of the company’s newest notebooks. Here’s what you need to know about the industry’s latest connection standard.

What is Thunderbolt?

Thunderbolt (previously called Light Peak) is a new peripheral-connection technology, developed by Intel with collaboration from Apple, that combines data, video, audio, and power in a single connection. Based on the PCI Express and DisplayPort architectures, Thunderbolt allows for high-speed connection of peripherals such as hard drives, RAID arrays, video-capture solutions, and network interfaces, and it can transmit high-definition video using the DisplayPort protocol. Each Thunderbolt port also provides up to 10 Watts of power to connected peripherals.

Is Thunderbolt any different from Light Peak?

Light Peak was simply Intel’s codename for Thunderbolt while the technology was under development—they’re names for the exact same technology. One thing to note, however, is that although Thunderbolt is designed to allow the use of either electrical or optical connections, Apple’s current implementation uses only electrical circuitry, which allows the port to carry power, as well. (Intel expects most vendors to use electrical connections both for this advantage and because of the lower cost. Optical versions will likely be used only when cables longer than three meters are needed.)

So how does this involve PCI Express?

PCI Express is the high-speed architecture that’s used to connect many of the components in your Mac, such as the processor, graphics card, and hard drive. You can think of PCI Express as an expressway that lets data move quickly and efficiently between these “locations.” Because Thunderbolt is based on PCI Express, it offers a direct connection to the PCI Express bus, which is part of the reason it can offer such impressive performance.

How fast is it really?

In theory, it’s blazing fast. A Thunderbolt channel can provide up to 10 Gigabits per second (Gbps) of data throughput—and each Thunderbolt port includes two channels. Thunderbolt is also bi-directional, meaning it can transmit and receive data at the same time. Even with estimated real-world performance of around 8Gbps, Thunderbolt is many times faster than FireWire 800 and USB 3.0. It’s also significantly faster than the eSATA connections available on many Windows PCs.

Of course, just as with previous high-speed interfaces, performance of each connected device will often be much lower thanks to the limitations of the device itself; for example, most SATA hard drives top out at 3Gbps, and even SATA 3.0 drives are limited to a theoretical 6Gbps. Similarly, an older, slower device placed in the middle of the chain can—if not connected properly—cripple throughput for higher-speed devices connected after it. (More on that below.)

(Image courtesy Intel)

What are Thunderbolt’s advantages over current connections—FireWire, USB, eSATA, and the like?

The biggest advantage is obviously the aforementioned performance. But another big selling point is that, since Thunderbolt supports data, video, audio, and power, you can use a single Thunderbolt port—and thus a single cable—to connect many of your peripherals. Or at least you’ll be able to once you’ve got enough Thunderbolt devices and adapters.

So Thunderbolt is kind of like Apple’s old Apple Display Connector technology?

Not really, although the idea is similar to that of the Apple Display Connector (ADC). While Thunderbolt does carry video, audio, data, and power—thus reducing the number of cables sticking out of your computer—it doesn’t provide enough power to run a large display. (ADC could provide up to 100 Watts of power, along with video, audio, and USB signals.) On the other hand, an ADC connection required a specialized—and expensive—video card, whereas Thunderbolt uses the Mini DisplayPort standard.

The Thunderbolt connector

What type of physical connection does Thunderbolt use?

Conveniently enough, Thunderbolt uses a connector that fits the Mini DisplayPort port on all recent Macs. In fact, the newest MacBook models include only a Thunderbolt port—there’s no separate Mini DisplayPort port.

But how do I connect my display if there’s no Mini DisplayPort jack?

Because Thunderbolt handles both data and DisplayPort video, you connect your Mini DisplayPort-enabled display—or another display using a Mini DisplayPort adapter—to the Thunderbolt port, or you daisy-chain it to other Thunderbolt devices, as noted below.

How do Thunderbolt’s video and audio capabilities compare to DisplayPort’s?

Remember, every Thunderbolt port includes both DisplayPort and PCI Express connections. Which means a Thunderbolt port can handle the same types of video and audio—displays with greater than 1080p resolution and up to eight channels of audio—as a DisplayPort port. When it comes to video, the main limitation is your graphics card. For example, the new MacBooks support an external display up to 2560 by 1600 pixels at millions of colors, in addition to the built-in display in either mirroring or dual-display mode. On a desktop Mac, the Thunderbolt port would support two high-resolution displays. You can connect a Mini DisplayPort-enabled display directly, or a DisplayPort, HDMI, DVI, or VGA display using an adapter.

Is Thunderbolt backward-compatible with USB and FireWire?

Third-party vendors will sell adapters, available sometime this spring, that let you connect USB, FireWire 400, and FireWire 800 devices to Thunderbolt ports. Thunderbolt won’t make these legacy devices any faster, however—they’ll still be limited to the performance of their built-in components. For example, a FireWire 800 device still won’t be able to transfer data faster than 800 Mbps.

What about other types of connections?

As noted above, Thunderbolt can carry data, video, audio, network data, and power, so we also expect to see adapters providing audio and Ethernet connections. Perhaps we'll even see cables that grab power from the Thunderbolt port—this could be useful, for example, for getting some extra juice for an external USB or FireWire peripheral.

Can I connect multiple devices to a single Thunderbolt port?

You can connect up to six devices to each Thunderbolt port by daisy-chaining them—connecting the first to the Thunderbolt port, connecting the second to the first, and so on. Of course, this requires that each device in the chain have two Thunderbolt ports (or two other types of data ports along with Thunderbolt adapters)—one to connect to the device in front of it and one to provide a connection for the device after it.

Does connecting multiple devices affect performance, as it can with USB 2.0?

Unlike with USB 2.0, where connecting a non-Hi-Speed device or a USB 1.0 device can affect the performance of the entire USB bus, Thunderbolt is designed to handle multiple devices of varying levels of performance without affecting the channel itself. Of course, those devices still share the total throughput of the Thunderbolt channel, which could limit the performance of a particular device if multiple devices are transferring lots of data at the same time, but the performance of the Thunderbolt channel itself shouldn’t be affected.

How does connecting non-Thunderbolt devices affect performance?

It depends. If you connect those devices to the end of your Thunderbolt chain, they should’t adversely affect the performance of faster “upstream” devices. If you connect non-Thunderbolt devices in the middle of a Thunderbolt daisy chain, the way you connect them matters.

For example, if you use two FireWire-to-Thunderbolt adapters to put a FireWire hard drive in the middle of a Thunderbolt daisy chain, the performance of the rest of the chain "downstream" from the computer will be limited by the FireWire drive’s FireWire bus, which simply can’t pass data as fast as Thunderbolt.

However, it’s likely we’ll see specialized adapters and hubs that preserve the Thunderbolt chain while branching off to provide USB, FireWire, Ethernet, video, or audio connections. These could range from simple, T-shaped adapters that provide Thunderbolt input and output along with a single legacy connection, to multi-device hubs that let you connect several legacy devices (docking station, anyone?). When using one of these specialized adapters, the higher performance of the rest of the Thunderbolt chain should be preserved.

Until such adapters are available, one of the biggest Thunderbolt challenges will be that your display must be the last device in the chain, because the new MacBooks have only a single Thunderbolt port and current displays—even those with DisplayPort connections—don’t have a way to pass data on to another device. This will make it a hassle if you want to temporarily connect or disconnect, say, a Thunderbolt hard drive, as you’ll need to disconnect your display in the process.

We suspect that, with the exception of displays, most people will choose to connect their existing peripherals to their computer’s USB, FireWire, Ethernet, and audio ports.

Can you boot a Mac from a Thunderbolt drive?

We suspect so, but we haven't yet confirmed this capability. We'll update this answer when we know more. We're also looking into whether you can boot your Mac from a USB or FireWire drive connected to a Thunderbolt port using an adapter.

Does Thunderbolt support Target Disk Mode and Migration Assistant?

On the new MacBook Pro models, you can use Target Disk Mode over a computer-to-computer Thunderbolt connection. (We assume this will be the case with future Thunderbolt-equipped Macs, as well.) However, Mac OS X’s Migration Assistant software doesn’t currently support Thunderbolt connections.

Will all Macs get Thunderbolt?

Apple doesn't comment on future products, but it’s telling that the company has made Thunderbolt a standard feature across the entire MacBook Pro line—even the entry-level model. The company has said it expects wide adoption of Thunderbolt, and for that to happen, its spread across the Mac line seems like a given. As Apple updates the company’s other computer lines over the coming months, we expect to see Thunderbolt added to every Mac model. A more interesting question, though, is…

Will Thunderbolt eventually replace FireWire and USB on Macs?

Perhaps, although eventually could be a very long time. Thunderbolt is brand new, and as such it will be a while before it becomes anywhere near as commonplace as USB and FireWire. It’s expected to be widely adopted by vendors and peripheral makers over the next few years, but until most popular peripherals are available with Thunderbolt connections, we don’t expect these legacy connections to disappear entirely from the Mac lines.

That said, we all remember the original iMac, when Apple nixed legacy serial and ADB connectors in favor of USB—long before USB peripherals were commonplace and inexpensive—and we can imagine the idea of a single port and connector appealing to Apple and Steve Jobs. Just look at the dock-connector port that adorns the iPhone, iPad, and iPod touch. Speaking of which…

Will iOS devices get Thunderbolt?

As noted above, Thunderbolt relies on PCI Express, the architecture that underpins Macs and most PCs. But iOS devices don’t use a PCI Express architecture, which would presumably make it difficult to simply stick a Thunderbolt port on an iPhone. Plus the dock-connector port on iOS devices provides quite a bit of additional functionality—it’s got 30 connection pins for a reason, after all. Finally, it’s not clear what benefits Thunderbolt would provide that the dock-connector port is missing. We suspect it’s far more likely that Apple will eventually sell an optional Thunderbolt-to-dock-connector cable for charging and syncing.

Are there any Thunderbolt peripherals available yet?

Thunderbolt just became official, and while a number of vendors have announced Thunderbolt-based peripherals, none are yet available. For example, Promise has announced the Pegasus Thunderbolt Technology DAS, a 4- or 6-bay external RAID array, and LaCie has announced a Thunderbolt version of the company’s Little Big Disk portable drive that features dual hard drives or SSDs (solid-state drives). These and other Thunderbolt peripherals are expected to be available beginning this spring.