Not all drives speak the same language, and these file systems decide who understands what.
When you purchase a new storage drive, it may tell you it needs reformatting, but which format is best? The main options for removable drives and memory cards these days are FAT32, exFAT, and NTFS, ...
The best FS for that would be exFAT, as it's compatible with both Lion and Win7. Less than half of the total space is used up, so I thought I'd be able to resize the partition with Disk Utility, ...