Zit Seng's Blog

A Singaporean's technology and lifestyle blog

From Mini DisplayPort to Thunderbolt

Apple is well-reputed to be forward-looking in the technologies it uses. Examples include the popularizing of USB ports and the abandoning of floppy disk drives. More recently, Apple has set out to replace Mini DisplayPorts with Thunderbolt ports in its product line, starting with the updated MacBook Pro announced on 24 Feb 2011.

Not many people are familiar with Mini DisplayPort to begin with, let alone Thunderbolt. If you, too, wonder what Mini DisplayPort looks like, it’s the fourth port from the left  in the photo above. Macs have been using Mini DisplayPort  for many years in lieu of the more conventional VGA connector.

I recently did some reading up on DisplayPort, Mini DisplayPort and Thunderbolt. It turns out I didn’t know much about them either. I was curious about how these interface technologies compared with each other in terms of “bandwidth”.

Until now, I just used the Mini DisplayPort on my MacBook Pro (MBP) because, well, that was the only way I could get external video out of it. It was rather convenient to carry around the Mini DisplayPort to VGA adapter too. So what’s so great about Mini DisplayPort and why are we moving on to Thunderbolt?

It turns out that DisplayPort is quite a “power” interface. It’s not a general purpose data interface, but one designed specifically to carry digital video (and later, also audio) to an external display. It is superior to DVI in that it carry delivery video resolutions up to 2560×1600 (Mini DisplayPort) or 3840×2160 (DisplayPort). There are adapters from Mini DisplayPort to VGA, DVI and HDMI. DisplayPort version 1.2, available on the MBP introduced in early 2010, supported a uni-directional data rate of 20 Gbps.

Why move on to Thunderbolt? Before we go on, I just want to point out that Thunderbolt remains backward compatible with Mini DisplayPort, even to the extent of retaining the same physical port dimensions and electrical interfaces. Apple made sure of that. The Thunderbolt technology was originally developed by Intel, which had called it Light Peak, and had meant to use an optical transmission medium. But thanks to Apple’s influence, it eventually emerged being completely backward compatible with Mini DisplayPort. An optical transmission medium is still being worked on for future versions of Thunderbolt.

Thunderbolt is a general purpose data interface, something like, say, USB. Technically, it is actually a combination of computer expansion bus (PCI Express, specifically), and DisplayPort, carried over a single serial interface. When connected to a DisplayPort device, the Thunderbolt connection provides up to 20 Gbps (21.6 Gbps) of output. When connected to a Thunderbolt device, the Thunderbolt connection provides 20 Gbps of bi-directional data transfer.

In terms of data rate, Thunderbolt isn’t quicker than DisplayPort, but the former supports bi-directional data. This effectively doubles the bandwidth in Thunderbolt. The most important thing, though, is that Thunderbolt can be used as a general purpose data interface, such as connecting to external hard disks and Gigabit Ethernet dongles. Similar to USB, Thunderbolt can be connected through a hub, although the latter supports only a maximum of 7 devices.

Should we look forward to Thunderbolt? It’s plenty useful, so I’d think the answer is yes. Thunderbolt can function as a a very convenient “docking” connector, seeing that it combines both data and video. Imagine how convenient it’ll be when you can dock your notebook with a single connector and get instant access to external display, Gigabit Ethernet, and external hard disks. (If only it can also carry enough power to drive a notebook!) There are even external Thunderbolt GPUs if your notebook doesn’t have enough horsepower.

The trouble with Thunderbolt right now is that devices are still relatively costly. They are also not plentiful, nor easily available, and not many computers come with Thunderbolt ports. So while it is an exciting technology, it is still relatively immature, even though it’s been commercially available for over a year.

USB 3.0, while slower at 5 Gbps, might just be a little more interesting to more people. It’s definitely helped along by the ubiquity of USB, and backward compatibility with older USB devices. But unless USB comes up with something faster sooner than later, our need for greater speeds might drive us to Thunderbolt.

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