| Type | Dual-protocol I/O[1] | ||
|---|---|---|---|
| Production history | |||
| Designer | Intel and Apple[2] | ||
| Manufacturer | Various | ||
| Produced | February 2011–present | ||
| General specifications | |||
| Length | 3 meters maximum (copper)[3] | ||
| Width | 7.4 mm male (8.3 mm female) | ||
| Height | 4.5 mm male (5.4 mm female) | ||
| Hot pluggable | Yes | ||
| Daisy chain | Yes, up to 7 devices[3] | ||
| External | Yes | ||
| Connector | Mini DisplayPort | ||
| Electrical | |||
| Signal | 10 W[3] | ||
| Data | |||
| Data signal | Yes | ||
| Bitrate | 20 Gbit/s PCIe and DisplayPort bi-directional 100 Gbit/s (over next decade)[4] |
||
| Protocol | PCI Express, DisplayPort v1.1a[3] | ||
Thunderbolt (originally codenamed Light Peak[1]) is an interface for connecting peripheral devices to a computer via an expansion bus. Thunderbolt was developed by Intel and brought to market with technical collaboration from Apple Inc. It was introduced commercially on Apple's updated MacBook Pro lineup on February 24, 2011, using the same port and connector as Mini DisplayPort. Though initially registered with Apple Inc., full rights of the Thunderbolt technology trademark belong to Intel Corp., and subsequently led to the transfer of the registration.[5]
Thunderbolt combines PCI Express and DisplayPort into a serial data interface that can be carried over longer and less costly cables. Thunderbolt driver chips fold the data from these two sources together, and split them back apart again for consumption within the devices. This makes the system backward compatible with existing DisplayPort hardware upstream of the driver.
The interface was originally intended to run on an optical physical layer using components and flexible optical fiber cabling developed by Intel partners and at Intel's Silicon Photonics lab. The Intel technology at the time was marketed under the name Light Peak,[6] today (2011) referred to as Silicon Photonics Link.[7] However, it turned out that conventional copper wiring could furnish the desired 10 Gbit/s Thunderbolt bandwidth per channel at lower cost. Later versions of Thunderbolt are still planned to introduce an optical physical layer based on Intel silicon photonics technology.
The Intel and Apple implementation of the port adapter integrates PCI Express data and DisplayPort data, allowing them to be carried over the same cable simultaneously. A single Thunderbolt port supports hubs as well as a daisy chain of up to seven Thunderbolt devices; up to two of these devices may be high-resolution displays using DisplayPort.[8]
Apple sells existing DisplayPort adapters for DVI, dual-link DVI, HDMI, and VGA output from the Thunderbolt port, showing broad compatibility.
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Intel introduced Light Peak at the 2009 Intel Developer Forum (IDF), using a prototype Mac Pro motherboard to run two 1080p video streams plus LAN and storage devices over a single 30-meter optical cable with modified USB ends.[9] The system was driven by a prototype PCI Express card, with two optical buses powering four ports.[10] At the show, Intel claimed that Light Peak-equipped systems would begin to appear in 2010.[11] A Youtube video simultaneously published by Intel also showed Light Peak interfacing with HD cameras, laptops, docking stations, and HD monitors. Jason Ziller, Head of the Intel Optical I/O Program Office also demonstrated the internal components of the technology under a microscope and the outputing of data through an oscilloscope.[12]
On 4 May 2010, in Brussels, Intel demonstrated a laptop with a Light Peak connector, indicating that the technology had shrunk small enough to fit inside such a device, and had the laptop send two simultaneous HD video streams down the connection, indicating that at least some fraction of the software/firmware stacks and protocols were functional. At the same demonstration, Intel officials said they expected hardware manufacturing to begin around the end of 2010.[13]
In September 2010, some early commercial prototypes from manufacturers were demonstrated at Intel Developer Forum 2010.[14]
Originally conceived as an optical technology, Thunderbolt switched to electrical connections to reduce costs and to supply up to 10W of power to connected devices.[15]
In 2009, Intel officials said the company was "working on bundling the optical fiber with copper wire so Light Peak can be used to power devices plugged into the PC."[16] In 2010, Intel said the original intent was "to have one single connector technology" that would allow "electrical USB 3.0 […] and piggyback on USB 3.0 or 4.0 DC power."[17]
In January 2011, Intel's David Perlmutter told Computerworld that initial Thunderbolt implementations would be based on copper wires.[18] "The copper came out very good, surprisingly better than what we thought," he said.[19]
Intel and industry partners are still developing optical Thunderbolt hardware and cables.[20] The optical fiber cables are to run "tens of meters" but will not supply power, at least not initially.[21][22][23] They are to have two 62.5-micron-wide fibers to transport an infrared signal up to 100 metres (330 ft).[24] The conversion of electrical signal to optical will be embedded into the cable itself, allowing the current DisplayPort socket to be future compatible, but eventually Intel hopes for a purely optical transceiver assembly embedded in the PC.[23]
It was long rumoured that the early-2011 MacBook Pro update would include some sort of new data port, and most of the speculation suggested it would be Light Peak.[25] At the time, there were no details on the physical implementation, and mock-ups appeared showing a system similar to the earlier Intel demos using a combined USB/Light Peak port.[26] Shortly before the release of the new machines, the USB Implementers Forum (USB-IF) announced they would not allow this, stating that USB was not open to modification in this way.
In spite of these comments and speculation, the introduction came as a major surprise when it was revealed that the port was based on DisplayPort, not USB. As the system was described, Intel's solution to the display connection problem became clear: Thunderbolt controllers fold data from existing DisplayPort systems with data from the PCI Express port into a single cable. Older displays, using DisplayPort 1.1 or earlier, have to be located at the end of a Thunderbolt device chain, but newer displays can be placed anywhere along the line.[22] Thunderbolt devices can go anywhere on the chain. In this respect, Thunderbolt shares a relationship with the older ACCESS.bus system, which used the display connector to support a low-speed bus.
Apple published[27] technical details explaining that 6 daisy-chained peripherals are supported per Thunderbolt port, and that the Display should lie at the end of the chain.
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In February 2011, Apple introduced its new line of MacBook Pro laptop computers and announced the technology's commercial name would be Thunderbolt, with these machines being the first to feature the new I/O technology.
In May 2011, Apple announced a new line of iMacs that include the Thunderbolt interface.[34]
The Thunderbolt port on the new Macs is in the same location relative to other ports and maintains the same physical dimensions and pin out as the legacy Mini DisplayPort connector. The primary visual differentiation on Thunderbolt equipped Macs is a Thunderbolt symbol instead of a DisplayPort symbol next to the port opening.[8]
The DisplayPort standard is partially compatible with Thunderbolt, as the two share Apple's physically compatible Mini DisplayPort connector. The Target Display mode on iMacs requires a Thunderbolt cable to accept a video-in signal from another Thunderbolt-capable computer.[35] Mini DisplayPort monitors function correctly as an external monitor without an adaptor if they are either the only or the last device in the Thunderbolt device chain.
Intel announced that a developer kit would be released in the second quarter of 2011,[36] while manufacturers of hardware development equipment have indicated they will add support for the testing and development of Thunderbolt devices.[37] The developer kit was not yet available as of 21 July 2011[update], with Intel saying that interested parties needed to keep checking later.[38]
Thunderbolt is based on the Mini DisplayPort connector developed by Apple. This is electrically identical to "normal" DisplayPort connectors, but uses a smaller connector that is more suitable for use on laptops and other consumer devices. It is expected that Thunderbolt's use of this connector will drive wider acceptance.
Because the PCIe bus does not carry video data, it is unclear whether a standalone PCIe card could offer a Thunderbolt port. The Intel Thunderbolt Technology Brief does not give a conclusive answer.[3] Intel disclosed documentation where video stream is sent to a dual-thunderbolt controller, with the video stream being only sent to one of the Thunderbolt Port, giving the assumption that video stream is not mandatory on Thunderbolt implementation.
Thunderbolt can be implemented on PCIe graphics cards, which have access to DisplayPort data and PCI express connectivity, or on the motherboard of new devices, such as the MacBook Pro.[8][22][39]
Thunderbolt controllers on the host and peripherals multiplex the PCIe and DisplayPort data into packets at the transport layer and demultiplex them at the destination.[3]
Thunderbolt is interoperable with [DisplayPort] 1.2 compatible devices. When connected to a DisplayPort compatible device the Thunderbolt port can provide a native DisplayPort signal with 4 lanes of output data at no more than 5.4 Gbit/s per lane. When connected to a Thunderbolt device the per-lane data rate becomes 10 Gbit/s and the 4 lanes are configured as 2 channels with each bidirectional 10 Gbit/s channel comprising one lane of input and one lane of output.[3]
Since Thunderbolt extends the PCI Express bus, which is the main expansion bus in current systems, it allows very low-level access to the system. PCI devices need to have unlimited access to memory, and may thus compromise security.[40] This issue exists with many high-speed expansion buses, including PC Card, ExpressCard and the IEEE 1394 interface, commonly known as FireWire.
It is worth noting that a number of Intel processors since the introduction of the Nehalem microarchitecture (that is, a number of CPU branded Core i5, Core i7, or later) support VT-d, an IOMMU implementation. This allows the operating system (OS) to isolate a device in its own virtual memory address space (in a manner analogous to the isolation of processes from one another using the MMU). Devices are thus prevented from having access to all of physical memory.
As of July 2011, the first two meter Thunderbolt cable from Apple costs US$49.00.[41] As an active cable, it includes circuitry inside the connectors. The cable has 5 wires, 1 for management and two uni-directional pairs, one for incoming and second for outgoing traffic.[42]
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