This has nothing to do with your CPU not having 64bits, this is just a software thing. Complain at the vendors of video software that don't handle such large files, if you need someone to blame. Your operating system, file system and CPU seem to be up to handling 64bit file pointers, otherwise that 12GB file wouldn't exist. Since it's an AVI file, look on the web for file splitters, there are a couple of them. Maybe one of them is able to cut it into smaller chunks. What program created that 12GB file in the first place anyway?