so i have an external 2tb drive and used up 1.5tb space. my mac reads i still have 500gb left. the drive is fat32 but when i plugged the drive into my friends windows it reads not much space left and is pretty much already full and when i tried to move some files over to my friends windows, it wouldnt move correctly why does mac read it different and how will i know when space is really full?
Is there a chance you've deleted files on the mac side but failed to empty the trash? I don't think that would be the case, but I've forgotten to do that a few times.
Since osx 10.6, OSX has used a base 10 numbering system (1 MB = 1000 bytes) for disk space. Windows still uses base 2 (1 MB = 1024 bytes). It has absolutely nothing to do with file systems. Essentially, they use different ways to measure disk space. The same amount is being used and is free, but it is calculated differently.
I'm not 100% sure, but I don't think this is the case. I thought about this as well, but the space free wouldn't be so different. In OSX, it will be something like 2tb disk with 1,500,000 MB used 500,000 MB free. Windows would be somewhere around 1,800,000 MB. But you would also have to remember that the 1,500,000 MB used on the mac side would then be reduced as well to something smaller due to the change in reading size with 1024 bytes instead of 1000 bytes. He/She should still have free space.
I am guessing you didn't understand what I wrote. I'm not arguing that Mac OS x reads it different, I am just saying that when you switch to the windows side, it's going to reduce the total capacity as well as the used capacity. A 2 Gb file on the Mac side means the true file size is around 2000 mb, when you connect it to windows and view the properties, it will show a file size of 1.8 or 1.9 Gb maybe.
What does your friend's computer show for used/free space this could help diagnose the issue. For the issue of "wouldn't move correctly" was there an error message? If not, what was the issue? You might want to try Verify Disk from Disk Utility to see if there are any issues on the disk in question. The stuff in the trash counts as space used, so this won't be the issue.