

Lion’s AirDrop feature is supposed to cut through all that nonsense and make moving one or more files between two computers a breeze. You just open the AirDrop window (click its name in the sidebar of any Finder window), and drag files onto the icon of a nearby user (who also has the AirDrop window open). They agree to accept the files, and—voilà!—the transfer happens.

But how does AirDrop accomplish this apparently seamless magic? By taking advantage of a not-so-new bit of Wi-Fi technology that allows computers and other devices to connect to one another via peer-to-peer networking. Computers connecting via AirDrop don’t have to be connected to the same Wi-Fi network. They don’t require an ad hoc network or software base station. AirDrop bypasses all that.

The right chips

What AirDrop does require is a Mac with one of the newer Wi-Fi chips—specifically, those that support the Wi-Fi Direct networking system (or similar technology that predates its standardization). Wi-Fi Direct has been around in industry-approved form since 2009. It enables devices to establish simple peer-to-peer connections; at the same time, it supports strong WPA2 encryption. It also allows devices to advertise their available services to other pieces of hardware. For instance, a printer with Wi-Fi Direct could broadcast the fact that it was a printer—even its model number for the purposes of loading a driver—while a cell phone might tell nearby devices that it can transfer files and be used as a relay to access the Internet.

Most popular Wi-Fi chipsets—including some that Apple has used for years—support Wi-Fi Direct. But even though Apple and Microsoft sit on the board of the Wi-Fi Alliance, which developed the underlying technical standards and certification regime, support in operating systems has been lacking. You can’t find it Windows 7 or Lion, nor in any mobile operating system. For AirDrop, Apple is using just a subset of Wi-Fi Direct’s features; strictly speaking, AirDrop isn’t actually compatible with the standard.

Apple began to include compatible Wi-Fi chips in some of its Macs three years ago; but as recently as a year ago, some Mac models still didn’t have them. Unless your Mac has the correct Atheros or Broadcom chip, you can’t use AirDrop. Apple’s AirDrop troubleshooting page lists the Macs that support the technology:

  • MacBook Pro (Late 2008 or newer, but not 17-inch Late 2008)
  • MacBook Air (Late 2010 or newer)
  • MacBook (Late 2008 or newer, but not white MacBook Late 2008)
  • iMac (Early 2009 or newer)
  • Mac Mini (Mid 2010 or newer)

Of my five home and work Macs, only two have the right chips, even though they all meet Lion’s other hardware requirements.

The hit-or-miss availability of AirDrop has made some Mac owners mad, and they’ve been venting their spleen in online forums and news stories. People rightly complain when a marquee feature of a new OS isn’t available uniformly. Some have wondered why Apple didn’t make AirDrop available over older Wi-Fi or on Ethernet connections. The answer is that AirDrop isn’t based on standard networking technologies; it’s peer-to-peer. Apple would certainly have made more friends by adopting the approach of DropCopy ( Macworld rated 4 out of 5 mice , free for one to three computers), which runs on standard network connections or over Bonjour.

Despite its shortcomings, I see AirDrop as a sign of things to come. As more new Macs are sold and old ones die or are put out to pasture, more and more machines will support AirDrop. As modern networking chips become more common, Apple (and others) could implement Wi-Fi Direct fully, which would make a host of common networking tasks simpler. AirDrop (or Wi-Fi Direct) could also find its way into iOS and other mobile operating systems. However it happens, we’re likely to find AirDrop-style peer-to-peer hookups more routine and more consistently available as time goes on.