Windows, Mac, and Unix all keep files in different formats. When transferring files between the two platforms, it is important to transfer binary files (such as graphics) in Binary mode, preserving their format, and text files (such as scripts) in ASCII format.

Most FTP Clients allow you to specify a transfer mode of Binary, ASCII, or Auto. Unfortunately, the behaviour of the Auto transfer mode differs between FTP Clients. The most reliable way to upload files is to specify which files should be uploaded in Binary, and which in ASCII.

If you transfer a script file in Binary mode by mistake, you will most likely receive a 500 Server Error when you try to execute the program with your Web Server. If you transfer a graphic file in ASCII mode by mistake, the image will be corrupted and it will probably appear as broken.