I have a 3TB WD external hard drive. I've formatted this with disk utility and separated it into 2 partitions: one is for time machine backups, the other is for long term storage (basically an archive for my old projects and things of that nature). My question is: will the archive mount and operate properly on a windows computer? In other words, will I be able to plug the drive into both my iMac and my Windows PC to be able to archive projects from both?
You must have Mac OS X 10.6.5 or newer, and PCs need to be Windows Vista. Although it is possible to format a drive as exFAT from Disk Utility on the Mac,. Since the release of Mac OS 10.3 'Panther' in 2003, Mac computers have had the ability to read the data on hard drives formatted with the Windows NTFS file system.
Thanks for your time, and pardon my ignorance on this topic. My advice (my opinion only, others' will be different): If you value those projects you're storing on the external drive, DO NOT use any other formatting scheme than HFS+, GUID partition format. If you want to access those files on the PC side, there are solutions available that will let you mount a Mac-formatted drive in Windows.
I've never had need to do that, but I believe one of them is called 'Mac Drive'. I have too often seen postings here from users who had data stored on a drive that was 'cross-formatted' (for both Mac and PC), and after connecting it to the PC, at some point the data just went. Gone (at least on the Mac side). Keep important Mac stuff on a Mac formatted drive. If you need a 'cross-platform' drive, use a THIRD, cross-formatted drive to 'carry between' the two computers.
A high-capacity USB flashdrive can serve this purpose well. Again, my opinion only.