What version of the MacOS is pre-installed on the White Intel iMac models?

All White Intel iMac models shipped with a version of MacOS X 10.4 "Tiger".

For particular build numbers, please refer to "MacOS: Builds Included with Intel Macs" from the Apple Support Site.

Can the White Intel iMac models run MacOS X applications written for PowerPC Macs?

A good percentage of MacOS X applications written for PowerPC-based systems can run on the Intel-based iMac systems, and other Intel-based Macs, using the "Rosetta Universal Binary Translator", but as one would expect, these applications will run more slowly than they would if they were "native" for Intel-based processors.

The always excellent MacInTouch [no longer online] prepared a list of "Universal Binary" applications that will run natively on Intel-based Macs. The same website also has a list of applications written for the PowerPC with readers opinions regarding their performance using "Rosetta". You may wish to consult these lists to ensure compatibility with any particular application of interest [no longer online].

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

Can the White Intel iMac models run MacOS 9/Classic applications?

Apple provides no support for running MacOS 9 or the "Classic Environment" on any Intel-based Mac. The Intel-based iMac systems rely on the "Rosetta Universal Binary Translator" to run software for MacOS X for PowerPC, and this emulator cannot run "Classic/MacOS 9" applications.

If you have a mission critical application that only runs on MacOS 9, you likely would be best served by maintaining a PowerPC-based Mac. However, you may also be interested in reading "Are there any third-party programs to run MacOS 9/Classic applications on Intel Macs?" from the MacOS 9/Classic Support Q&A.

Can the White Intel iMac models run Windows?

Yes. For those unfortunate ones condemned to use Windows, the Windows on Mac Q&A provides answers for just about everything you need to know about running Windows on the White Intel iMac models or any other Intel-based Mac.

Can the White Intel iMac models run Linux?

Yes. The Intel-based iMac systems are 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.