machines run in user mode, twoOStwo itself requires installing various device drivers in the host operating system. Features Besides bridging to network adapters, CD-ROM readers and hard disk drives, twoOStwo also provides the ability to simulate some hardware. For example, an ISO image can be mounted as a CDROM and .hdd files can be mounted as hard disks. See also Parallels Workstation SVISTA VMware User Mode Linux Xen Comparison of platform virtualization software Virtualization software