What version of MacOS X is pre-installed on the MacBook Air? Can it run older Mac software?

The MacBook Air ships with MacOS X 10.5.1 (9B2324) pre-installed. It can run all Mac software written for Intel-based Macs and the vast majority of MacOS X applications written for PowerPC-based systems using the "Rosetta Universal Binary Translator". However, MacOS X applications that run via "Rosetta" will be slower than if they were "native" for Intel-based processors, as one would expect. MacOS 9/Classic applications are not supported.

For more on Rosetta, please refer to "What is Rosetta? What does it support?" from the "Macintel" Q&A.

For more on MacOS 9, please refer to "Are there any third-party programs to run MacOS 9/Classic applications on Intel Macs?" from the MacOS 9/Classic Support Q&A.

How do you install software on the MacBook Air without an optical drive?

The MacBook Air does not have an internal optical drive, and as such, to install software or transfer files from a CD or DVD one has to either purchase the external MacBook Air SuperDrive for US$99 or use the new "Remote Disk" function. Essentially, you can install the "Remote Disk" software on a nearby Mac or Windows box, and then "borrow" its optical drive to install software or transfer software via CD or DVD.

Additional information is available via the Apple Support Site and on page 15 of the MacBook Air User's Guide. It is worth noting that this can be used to re-install the operating system and use Apple Hardware Test for troubleshooting, but some copy-protected CDs, DVDs, and games cannot be installed using this method.

Can the MacBook Air play DVD movies via remote disk from another computer?

No. Unfortunately, it is not possible to play DVD movies -- or other optical media (CDs or games) -- that have copy-protection via Remote Disk from another computer.

Can the MacBook Air run Windows? Can you install Windows without the external optical drive?

Like all other Intel-based Macs, the MacBook Air is capable of running Windows. However, it is not possible to install Windows using Boot Camp via Remote Disk, and as such, an external optical drive is required to install Windows on the MacBook Air.

For more information regarding Windows on the Mac, please refer to the extensive Windows on Mac Q&A.

Can the MacBook Air run Linux?

Of course. The MacBook Air is capable of running a number of Intel-based distributions of Linux through Apple Boot Camp or by using "virtualization".

For more on Boot Camp and Virtualization, please refer to the Windows on Mac Q&A.