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UltraISO is an application for Microsoft Windows for creating, modifying and converting ISO image files used for optical disc authoring.
Initially UltraISO was shareware however since 2006 it has turned 'Pro' and become chargeable. The 'Free Trial' version is limited to ISO images of 300Mb or less 
UltraISO is currently produced by EZB Systems.
- Duplicate CDs and DVDs to an ISO image.
- Create ISO images from files located on a CD/DVD-ROM or hard disk.
- Edit existing ISO files by adding, deleting, and creating files and folders.
- Create compressed zisofs (.ISZ) images
- Create bootable CD, DVD and floppy images.
- Create a bootable USB flash or hard drive from a bootable disc image (works only with DOS, Windows NT and syslinux boot sectors).
- Converts: .BIN, .IMG, .CIF, .NRG, .BWI, .DAA, .DMG, .HFS and other formats to the standard ISO image.
- Supports all ISO 9660 levels and the Joliet extension.
- Optimization of ISO image file structures to save disc space.
- Capable of mounting only ISOs to a virtual drive.
- Create checksums for data verification of ISOs.
- Multiple language support.
- Built in digital audio player.
- Supports UDF disc format and allows creation of bootable UDF disks.
UltraISO uses a proprietary format known as ISZ. The format advertised as "ISO Zipped", even though it is not a simple zip archive. The format uses zlib or bzip2 to compress the data, and can support AES encryption of various strength. The file format specification is available publicly on EZB Systems's website. The format is now supported by third party applications such as Daemon Tools and Alcohol 120%.