Thunderbolt (code-named Light Peak): an overview
Update 2011-09-18: Thunderbolt news: plugs, optical cables, new chips, adoption by Acer and Asus
This post collects my previous material on Thunderbolt and adds new observations, now that it is officially out.
|The Thunderbolt logo. [Source: Intel]|
History. Quoting Apple and settling an old debate on who invented Thunderbolt:
Thunderbolt began at Intel Labs with a simple concept: create an
incredibly fast input/output technology that just about anything can
plug into. After close technical collaboration between Intel and Apple,
Thunderbolt emerged from the lab to make its first appearance in
Intel co-invented USB and PCI Express, which have become widely
adopted technologies for data transfer. Apple invented FireWire and was
instrumental in popularizing USB. Their collective experience has made
Thunderbolt the most powerful, most flexible I/O technology ever in a
|The Thunderbolt port on the new MacBooks. [Source: Apple]|
|Thunderbolt plugs are the same as Mini DisplayPort plugs. [Source: Intel]|
- Hybrid connector: Thunderbolt uses Mini DisplayPort connectors. A connected device either “speaks” Thunderbolt or is any existing Mini DisplayPort device (including adapters). It looks like you won’t need special Thunderbolt cables (if so, they would be downward-compatible with Mini DisplayPort). That is, wherever there is a Thunderbolt port, the following two standards are supported (see picture below).
- PCI express: Thunderbolt proper is based on it. This allows one to use existing PCI express drivers for many of the upcoming devices. There will be adapters for Gigabit Ehternet, Firewire, and eSATA devices.
- Mini DisplayPort: Existing adapters work with Thunderbolt ports. Good news for Apple owners, as Apple’s changing of video connector standards was getting tiresome.
- Speed: 10 Gbit/s. “It’s actually 2 channels, 10 Gbit/s bi-directional. So in summation you have potential for up to 20 Gbit/s upstream and 20 Gbit/s downstream, but any single device maxes out at 10 Gbit/s (you don’t ‘combine’ the two channels).” 
- One channel is dedicated to PCI express, the other one to
DisplayPort . The DisplayPort channel supports at most two displays
and drives the internal MacBook display. Thus, there can be at most one
external display. A way around this is to use PCI express to run the
display, but that will require a more sophisticated adapter.
- Copper now, fiber optics later: The current version of the standard uses copper cables, resulting in cheaper hardware and cables. Later versions will probably use fiber optics resulting in larger bandwidth and longer cables. The current limit is 3 meters, the later limit will be 100 meters.
- “[...] the port you'll find in new MacBook Pros and storage devices can actually take an optical
cable when those are cost-effective enough to roll out, because Intel
will eventually bake the optical transceivers into the cables
Advantages: Optical cables will be backward-compatible, current devices can use longer cables. Obviously, optical cables won’t make current devices faster.
- Power: 10 watts. Enough for charging an iPad and running external drives and burners. But not enough to run a notebook or a display. Compare :
- Firewire: 7 watts
- Apple’s high-power USB 2: 5.5 watts (enough for iPad charging)
- USB 3: 4.5 watts
- USB 2: 2.5 watts
- Daisy-chaining: One can daisy-chain up to 6 Thunderbolt devices. A DisplayPort device can always be added, because every Thunderbolt device supports it, but will always be last in line (unless it supports Thunderbolt). Devices can pass both data and power down the chain.
- Low latency: Important for professional video and audio applications.
|Diagram of Thunderbolt daisy-chaining. [Source: Intel]|
- HSPA (3G): 14 Mbit/s (down), 5.8 Mbit/s (up)
- LTE (4G): 100 Mbit/s (down), 50 Mbit/s (up)
- Wi-Fi 802.11n: 130 MBit/s
- Gigabit Ethernet: 300MBit/s (under real-world conditions)
- USB2: 480 Mbit/s (real world: ca. 200 Mbit/s)
- Fast hard drive: 80 MB/s (640 Mbit/s). RAIDs are obviously faster.
- Firewire 800: 786.432 Mbit/s
- Firewire 3200: 3.2 Gbit/s
- Fast SSD disk (flash memory): read 500 MB/s (4 Gbit/s), write 315 MB/s (2520 Mbit/s)
- Note that read speed approaches the limits of what USB3 can handle
- USB3: 4.8 Gbit/s.
- Thunderbolt: 10 GBit/s
USB3 is the closest competitor to Thunderbolt:
- Professional video and audio: Thunderbolt will replace Firewire in this domain. Apart from its low latency, its massive bandwidth are very important here, considering how large especially video files are.
- Fast computer networking. Thunderbolt can do master-to-master networking (USB3 can’t).
- Target disk mode: Firewire Macs can be booted into a special mode and used like an external hard drive. Thunderbolt can do the same .
- Docking stations: Because Thunderbolt can transport many
protocols (audio, video, etc.) at the same time, I expect it to get used
for future docking stations. It won’t carry enough power for laptops,
but tablets such as the iPad will be fine.
- Less cables between monitor and desktop computer: The monitor could have USB ports for keyboard and mouse and be connected to the desktop chassis via Thunderbolt and power. Thunderbolt would take care of video, audio, and USB.
- Mobile devices: The small ports are great for mobile computing. A single port for several tasks (docking stations!) is also useful.
- No booting from Thunderbolt (yet). 
With Intel’s and Apple’s weight behind Thunderbolt, things will become difficult for USB3. We now have an explanation why Intel dragged its feet in supporting USB3. USB3’s greatest advantage is that it is compatible with all current USB1 and USB2 devices. But it has the following disadvantages:
- Thick, relatively short cables. The current Thunderbolt standard has the same cable length limits as USB3, later versions will allow longer cables.
- No master-to-master communication, e.g. to connect two computers
- Unwieldy and fragile connectors (e.g. plugging in USB blindly is risky)
- Slower than Thunderbolt (less than half as fast). This will initially not be that big of a deal. USB3 will probably have a harder time increasing its bandwidth in the future.
- Won’t the Thunderbolt icon be mistaken for an electricity symbol?
- I wonder if the initial name was Lightning. After switching from fiber optics to copper, they had to rename it, but could at least keep the icon. (I’m only half joking.)
- Thunderbolt will bring to mobile devices and extensibility that is similar to what desktop computers currently offer.
First Thunderbolt products:
- Intel’s Thunderbolt page
- Apple’s Thunderbolt page
- A video demonstrating Thunderbolt daisy-chaining [uses the Thunderbolt code name “Light Peak”]
- MacBook Pro (early 2011) with Thunderbolt hands-on
- Thunderbolt smokes USB, FireWire with 10Gbps throughput
- Intel Thunderbolt: a closer look (updated with video)
- Intel refutes Apple exclusivity for Thunderbolt I/O, LaCie and Promise detail first Thunderbolt peripherals
“Apple doesn't actually have a timed exclusive on the technology [...]. [Intel] told us that while it's currently targeting an early 2012 launch for Thunderbolt with other OEMs – whereas the new MacBook Pro has Thunderbolt right now – there's nothing stopping other manufacturers from launching machines with the 10Gbps interconnect a good bit earlier if they so desire.”
- Intel Thunderbolt Rollout Won't Be Lightning Fast [First mention of Thunderbolt having two channels]
- Secrets of Thunderbolt and Lion [Explains in detail what Thunderbolt on Macs can and cannot do, clarifies how Thunderbolt’s two channels are used.]
- “Thunderbolt will allow splitters and other baroque configurations of adapters”