I'm almost 100% certain your thumb drive has a partition formatted as NTFS. Stock Mac OS X's NTFS driver only has the ability to read NTFS. It cannot write to NTFS. You could install the 3G FUSE NTFS driver for Mac OS, which would give that particular installation of Mac OS X on that particular computer the ability to read and write to NTFS. But if you go to another Mac that doesn't have that driver, you would again only be able to read your NTFS partition unless you again installed the 3G FUSE NTFS driver on that Mac, which would require that Mac's administrator password. Furthermore, NTFS is Microsoft's proprietary filesystem, just like HFS and HFS+ are Apple's proprietary filesystems. This means that open source drivers for those filesystems are more or less based off of reverse-engineering the filesystems, as I understand it. So they currently do not support all their features. And they don't even perfectly support the features they do support. Recently I have had issues with using NTFS on my external hard drive in Linux (don't need to go into detail here). So even the 3G FUSE NTFS driver (open source) won't give you 100% dependability (i.e, something bad might eventually happen). The solution is very simple: format the partition as FAT32. That is one of the most compatible filesystems of all time. Linux, Mac, Windows, and just about every OS can read and write and format FAT32 perfectly. It's been out for a very long time and it is well supported. In fact, just a couple days ago I formatted my mom's new thumb drive to FAT32 so it would be cross-compatible for her. I gave room for primary and secondary GPT headers and room for 33 sectors worth of primary and secondary partition table entries in case she decides to upgrade to GPT in the future, though right now it is pure MBR-structured (the switch could be done without loss of partitions or data therein). I also gave her a 64-sector partition for use as a BIOS Boot partition later on should she go there. Made the partitions align to clusters, and put a 200 MiB area of unallocated space between the partitions and between the partitions and the spaces for GPT stuff. Note that with FAT32 no one file can surpass 4 GB. That's not to say there aren't creative ways around that restriction. Jake
