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I have 4 GB USB drive and as I formated it with Mac OS X's Disk Utility in FAT format, it shows me 3.98 GB on my Mac but only shows me 200 MB on my Windows computer. Why this is so? What am I doing wrong on my Mac?

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up vote 6 down vote accepted

What does the Windows Disk Management program (enter diskmgmt.msc at a command prompt) show for this drive?

The 200 MiB size sounds to me as though you may have formatted your USB drive with GPT partitioning instead of MBR. In that case OS X may have slipped a 200 MB "EFI partition" ahead of your FAT partition. If Disk Management shows you that the USB drive uses GPT partitioning and there are two partitions, a 200 MiB partition followed by a 3,614 MiB (3.53 GiB) FAT partition, then that is what happened.

If that is the problem then I suggest you use MBR partitioning when you format on a Mac. Using Disk Utility before you apply the partitioning you would click on the "Options" button (underneath the "Volume Scheme" graphic to the right of the "+" & "-" buttons) and select "Master Boot Record".

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