What kind of video processor is provided by the MacBook Air models? What is the maximum resolution each can support on an external display?

All MacBook Air models have comparatively slow "integrated" graphics that share memory with the system.

The original MacBook Air has an Intel GMA X3100 video processor with 144 MB of shared DDR2 SDRAM. The "Late 2008/NVIDIA" and "Mid-2009" models have a NVIDIA GeForce 9400M video processor and the "Late 2010" models have a NVIDIA GeForce 320M video processor, all of which use 256 MB of shared DDR3 SDRAM. Finally, the current "Mid-2011" MacBook Air models have an Intel HD Graphics 3000 graphics processor that shares either 256 MB or 384 MB of DDR3 SDRAM.

The original MacBook Air is capable of simultaneously supporting 1920x1200 on an external display and all subsequent models are capable of supporting 2560x1600.

What is a "micro-DVI" port? How is it different from DVI and mini-DVI?

On basic terms, "micro-DVI" is even smaller than mini-DVI, which in turn, is smaller than the full-sized DVI. Even though micro-DVI is smaller than the mini-DVI provided by the "White and Black" MacBook models, it still is capable of supporting 1920x1200 on an external display in dual display or mirroring mode.

Diagram Credit: Apple, Inc.

For complete technical details of the micro-DVI port -- including signals and pin assignment -- please refer to the Video Developer Note from Apple.

Please note that micro-DVI is provided by the original MacBook Air model. Subsequently released models use a different standard called "Mini DisplayPort".

Also see: What is "Mini DisplayPort"? Is it an industry-standard? How is it different from or better than Mini-DVI and Micro-DVI?

What ports are provided by the MacBook Air models?

On the right of the original, "Late 2008" and "Mid-2009" MacBook Air models there is a small "trapdoor" that drops down to expose a standard speaker/headphone jack, a single USB 2.0 port, and either a micro-DVI or Mini DisplayPort connector (note that this door actually drops "down" from the underside of the computer rather than merely "flipping out" the side). On the left it has a MagSafe power connector -- but turned at a 90-degree angle to conserve space.

The "Late 2010" MacBook Air models lost the "trapdoor" and gained a USB 2.0 port. All have dual USB 2.0 ports, analog audio out and a Mini DisplayPort. The 13-Inch model also has an SDXC Card slot. The 45 W MagSafe power connector no longer is turned at a 90 degree angle either.

The current "Mid-2011" MacBook Air models share the same case and all ports as the "Late 2010" MacBook Air models replaced with one exception -- the MiniDisplay port has been swapped for a new "Thunderbolt" port that is capable of supporting external peripherals as well as an external display. Bluetooth 2.1+EDR connectivity, as is provided by all earlier MacBook Air models, also is upgraded to Bluetooth 4.0.

Those who need a greater number or variety of ports onboard -- more USB ports (hubs are available) or Firewire ports, for example -- probably would be better served by a MacBook or MacBook Pro.