What's included, what's not

A slower processor is not the only trade-off needed for the MacBook Air's ultralight design. Apple also ditched the optical drive. In that respect, the MacBook Air follows in the tradition of the earlier Apple subnotebooks - the Duo line from the early 1990s and the PowerBook 2400 from later in that decade. Neither contained an internal drive other than the hard drive. At the time, that meant a missing floppy drive.

The MacBook Air provides two options for accessing CDs and DVDs: an external USB SuperDrive that can read and write discs of all common formats, and a new technology called Remote Disk that allows the laptop to remotely access the optical drive of a Mac or PC using a wireless connection. One obvious concern: What happens if you need to boot from an alternate drive - for instance, when troubleshooting a hard drive or performing a clean install of Mac OS X? Apple's solution was to engineer the new laptop to support network booting using Remote Disk.

This solution - elegant in its simplicity for users - seems to be a natural outgrowth of the NetBoot technology that has allowed Macs to boot from a disk image hosted on a server for close to a decade. The use of the technology in the consumer space is impressive. NetInstall and related network-boot deployment technologies should also be supported with the MacBook Air, a big change from earlier Macs that required wired Ethernet for any form of network booting.

Although Remote Disk is an effective alternate boot solution, it does require access to another computer and network. This could be problematic when on the road, and it could limit the effectiveness of the MacBook Air as a user's lone computer. The optional USB SuperDrive (also engineered to be ultraportable and powered completely via USB) does provide an alternative. But Apple should consider providing the drive as a standard part of the MacBook Air package rather than requiring users to buy it separately.

Also gone but not forgotten are several ports common to today's Macs. The MacBook Air includes only a mag-safe power-adapter port (extra adapters cost £65), a single USB port, a micro Digital Video Interface (DVI) port for using external displays and a headphone jack. (Their design is innovative, particularly the flip-down panel for the USB and DVI ports and the headphones.)

FireWire? Gone. Ethernet? Ditto.

Given the common use of FireWire in Macs over the past several years - and the use of the FireWire port for Target Disk Mode, which allows a Mac's internal hard drive to be mounted as an external drive on another Mac and used by the Mac OS X Migration Assistant to transfer settings and files to a new Mac - it's particularly surprising that Apple elected to remove this port. But more ports mean a bigger logic board, so in this case, form won out over function.

The MacBook Air does sport an updated version of the Migration Assistant that can transfer files and settings via a wireless network, though performance may fall short of what is offered via FireWire when using Macs with slower wireless cards or an older wireless network.

Another missing port is Ethernet. Out of the box, the MacBook Air is a Wi-Fi-only machine. While this may be fine where Wi-Fi is common, it does present issues in environments where wireless networking is frowned upon. Often, physical network ports can be used to isolate specific network segments and limit or provide easy access to resources. Yes, this can theoretically be done with Wi-Fi, but doing so requires a more complex network design. As with the optical drive, a USB adapter is available as an add-on product if Ethernet is needed. That adapter is £19 (US$29).

Another difference that could rankle the faithful is that the MacBook Air's battery is built into the computer. This space-saving design prevents users from carrying multiple batteries and simply swapping in a fresh one when needed.

It also puts users in the same position as iPod and iPhone owners: As the battery ages and begins to lose its ability to hold a charge, there's no simple way to replace it. Given that users typically hold onto their computer investments for several years, this could pose a concern. Apple will make replacement batteries available for £139 in the UK - a substantial increase over the $129 US price, which is not far off the cost of a replacement battery for recent Mac portables.

Apple estimates that the battery will power a MacBook Air for five hours. Although such estimates are often optimistic, if true, that should help offset the inability to swap batteries on the road.