The universal rootstrust flash drives are called thus because they are compatible with all three desktop operating systems and support both 32-bit and 64-bit processors. That is no easy task, since there is no one file system type that is usable by all three. Windows and macOS have FAT32 in common. Linux can read from and write to a FAT32 partition, but can only execute a program, that resides on a Linux file system. The universal drives have a large FAT32 partition for rootstrust, the macOS and Windows versions of Java and plenty of space for your files. There is also a small Linux partition that is required for the Linux version of Java.