UltraISO, the disk imaging program, uses a proprietary format dubbed ISZ which is short for ISO Zipped. The format uses either ZLIB or BZIP2 to compress disc image data and can even be encrypted. The format can be mounted with Alcohol 120% and Daemon Tools.
UltraISO, as a program, has many different uses including creating ISO images from CD/DVD, creating images from files stored on an HDD, editing ISO files, creating bootable discs, converting other image files such as IMG file, BIN/CUE, BWI and DAA into ISO.
