External hard drives are dirt cheap, but what happens when you don’t want to carry multiple backup drives? Traditionally, the Time Machine drive on your Mac is formatted HFS+, something Windows doesn’t easily interact with unless you use third party software–and that can cost you. If you have a fairly large USB drive, such as 1TB or greater, you can set up special partitions in the drive to function with both Apple and Windows (or Linux, BSD, etc.).
Multi-purpose Time Machine
First, plug the hard drive into your Mac and open Disk Utility. Format the whole drive as HFS+ Journaled (NOT CASE SENSITIVE).
Afterwards, select the primary portion of the hard drive in your Disk Utility list (the uppermost one for your external), and then click on Partition.
Take the total size figure displayed and divide it by 2. Use that figure to split the disk in half, with one side being your HFS+ Time Machine and the other being an NTFS Windows Backup.
Once the partitioning is complete, go to your Apple -> System Preferences and click Time Machine. Select the ‘Time Machine’ disk that is half the size of your drive (or whatever you decided to give to your Mac). Let the backup run.
When your first backup is complete, you can plug it into a non-Apple computer and use the NTFS (Backup) partition for other storage. Out of the box, your Mac will have some NTFS support and you’ll see both Time Machine and Backup listed on your computer. Unfortunately, Apple doesn’t have all the NTFS support we’d like to see. You can use another filesystem for Windows if you wish (such as exFAT Filesystem)