If you move a hard drive between the two operating systems, here's what you need to know.
"I own a SimpleTech 320GB Black Cherry Hard Drive and needed it to run on both Mac and PC for school. I thought it would be pretty helpful if you made a video showing how to format a disc to run on all OS's using Mac OS X."
First, Here's why there's a difference. All data has to be put in a file format that the operating system can read off the hard drive. OS X uses a file format called HFS+ to write its data. Windows can't read or write HFS+ data natively. However, OS X and Windows both can read and write to a format called FAT32, which used to be used for Windows all the way back into the MS-DOS days. Most modern Windows systems use the NTFS file format, which OS X can read, but not write to.
So your best bet for compatibility is FAT32. Here's how to format a drive as FAT32. First, the Windows way and then the Mac way.
Plug in your external drive to the Windows machine. Go to My Computer and right-click on the correct drive letter. Make sure you are choosing the right drive! You're about to erase all data on the drive you choose.
Select format and choose format.
Under file system choose FAT 32.
Then press Start.
Pres OK to affirm you really want to destroy the data on this hard drive.
And sit and wait while it formats.
For OS X, connect your drive.
Launch Disk Utility. I usually just press Command-Space and type "disk utility" into Spotlight to find it.
Click on the drive you just connected. Again MAKE SURE you click on the right one.
Then Choose Erase. Remember, you are destroying every last shred of data on this USB drive.
Under Volume format, choose MS-DOS (FAT) That's FAT32. And then press erase.
And press erase again to confirm that you REALLY want to erase it.
Now here's the issue with FAT32. You cannot create a file larger than 4GB. If you're mainly working with Web pages or audio, that's fine. But if you're doing large video files, it's not going to work.
NTFS can handle files larger than 4GB, and OS X can read to it, it just can't write to it. There is way around that by using the free MacFUSE to help OS X to write to NTFS. See my video called Read and Write NTFS in OS X for more info on that.
You can also buy a program called MacDrive that lets Windows computers read MAC-formatted HFS+ drives.