Thunderbolt vs USB 3.0 vs eSATA

It's not very often that connection technologies make the news, but the arrival of Thunderbolt in Apple's new MacBook Pros has everyone asking crucial questions such as "what is it?", "how fast is it?" and "isn't that a terrible name for a kind of connection?"
So how does it compare with the other key interface standards, eSATA and USB 3.0?
Thunderbolt vs USB 3.0 vs eSATA: Speed
All three technologies are blazingly fast compared to USB 2.0, which tops out at 480Mbps.
eSATA delivers 3Gbps, with older eSATA 1.5 devices offering 1.5Mbps; USB 3.0, also known as Superspeed USB, goes up to 5Gbps; and Thunderbolt is a very respectable 10Gbps. As Intel puts it, that's enough to "transfer a full-length HD movie in less than 30 seconds".
Each Thunderbolt port is bi-directional and dual-channel, and devices can be daisy chained from a single connection. Potentially that means one device could be chugging data upstream at 10Gbps while another one sucks down data on the other channel at 10Gbps, although of course life is rarely that simple.
It's important to note here that these speeds are theoretical maximums, and there are all kinds of factors that will affect the speeds you actually get from connected devices.
Thunderbolt vs USB 3.0 vs eSATA: Compatibility
Thunderbolt combines two protocols, PCI Express (PCIe) and DisplayPort, which means you can connect monitors, external drives, video capture devices and so on. The DisplayPort element is backwards compatible, but you'll need a cable adaptor to connect an existing DisplayPort monitor.
USB 3.0 is backwards compatible, so you can connect USB 2.0 devices to a USB 3.0 hub and vice-versa, although of course you won't get USB 3.0 speeds.
eSATA is an external version of Serial ATA, the standard used for high-speed internal hard disk connections. As a result it's used for hard disks, hard disks and hard disks. Some firms, such as Toshiba, make laptops with dual-mode ports that can connect either eSATA or USB 2.0 devices.

What is Thunderbolt technology and how does it work

Developed by Intel (under the code name Light Peak), and brought to market with technical collaboration from Apple. Thunderbolt technology is a new, high-speed, dual-protocol I/O technology designed for performance, simplicity, and flexibility. This high-speed data transfer technology features the following:

• Dual-channel 10 Gbps per port
• Bi-directional
• Dual-protocol (PCI Express* and DisplayPort*)
• Compatible with existing DisplayPort devices
• Daisy-chained devices
• Electrical or optical cables
• Low latency with highly accurate time synchronization
• Uses native protocol software drivers
• Power over cable for bus-powered devices

Intel's Thunderbolt controllers interconnect a PC and other devices, transmitting and receiving packetized traffic for both PCIe and DisplayPort protocols. Thunderbolt technology works on data streams in both directions, at the same time, so users get the benefit of full bandwidth in both directions, over a single cable. With the two independent channels, a full 10 Gbps of bandwidth can be provided for the first device, as well as additional downstream devices.

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And all Thunderbolt devices share a common connector, allowing users to daisy chain devices one after another with interoperable cables.

What Thunderbolt means to users

Thunderbolt technology enables using the thinnest and lightest laptops and connecting to the extra power and performance of other devices when needed, using a single cable. Adding new performance devices is simple and easy—just plug and play—making Thunderbolt technology powerful and flexible.
Thunderbolt technology was specifically designed with professional audio and video applications in mind, where the inherently low latency and highly accurate time synchronization features play a crucial role.

Enthusiast–level performance expansion, now with a laptop

With Thunderbolt enabled products, video editing and sharing using Intel® Quick Sync Video technology is even faster and easier.
Data transfers for backup, sharing, and editing are tremendously accelerated using Thunderbolt products, significantly reducing times to complete these tasks.
And Thunderbolt enabled products are compatible with existing DisplayPort devices so you don’t have to go buy a new display to take advantage of a Thunderbolt technology enabled computer.

What does Thunderbolt technology mean for the PC industry

By tapping into the performance and protocols delivered over Thunderbolt technology, designers are free to innovate new PC products and configurations, no longer constrained to the boundaries of the chassis walls. Thunderbolt technology enables engineers to:

• Design standalone performance expansion technologies commonly used in desktops and workstations, using existing native device drivers and interconnected by a single cable.
• Introduce thinner and lighter laptops, expandable through Thunderbolt technology and its miniature connector designed for mobile applications, without sacrificing I/O performance.
• Extend to reach other I/O technologies by using adapters that use widely available PCI Express controllers. It's simple to create a Gigabit Ethernet, or FireWire, or eSATA adapters using existing device PCI Express drivers.

Thunderbolt products require a controller chip supplied by Intel and a small connector that would be included in platforms supporting this technology. The Thunderbolt controller chip provides protocol switching capabilities to support the two protocols over a single cable. Intel is making its controller chip available to the industry, and is working with other component manufacturers to deliver the Thunderbolt connectors and cables.

Thunderbolt vs USB 3.0 vs eSATA: Availability
Right now, only one firm makes Thunderbolt-enabled computers - Apple - and Thunderbolt-enabled peripherals such as hard disks are just starting to be announced. USB 3.0 devices - largely, but not exclusively, hard disks - are already available, and there are plenty of eSATA hard disks out there too.
Thunderbolt is largely an Intel technology and Intel clearly favours it over USB 3.0, so we'd expect Thunderbolt's profile to change quickly as Intel chucks its considerable weight behind the technology.
LaCie and Western Digital are already on board, and as Thunderbolt is fairly simple to engineer - if firms are already making PCIe or DisplayPort devices, it's relatively easy to make them into Thunderbolt devices - we'd expect to see lots of firms follow suit.

Is that bad news for USB 3.0? Not necessarily. The ubiquity of USB 2.0 means there are lots of USB devices out there, and USB 3.0 is turning up in everything from laptops to tablets.
There are already stacks of USB 3.0 devices on sale, and the presence of LaCie and Western Digital in the USB 3.0 market as well as the Thunderbolt one suggests we're looking at USB and FireWire all over again, with consumer devices going for USB and pro kit using the faster, less common standard.
And eSATA? Its advantages over USB 2.0 are obvious, but even if it matched internal SATA's move to 6Gbps speeds it'd still be significantly slower than Thunderbolt and only slightly speedier than USB 3.0. It's starting to look like a technology whose time is almost up.