Portable Ubuntu Remix is described as 'A portable image of Ubuntu that could run in Windows as a native win32 application. Adds capabilities to execute Linux applications and integrate with the Windows desktop' and is an app. There are three alternatives to Portable Ubuntu Remix for Windows and Linux. The best Portable Ubuntu Remix alternative is Knoppix, which is both free and Open Source. Other great apps like Portable Ubuntu Remix are Cooperative Linux and speedLinux.
Knoppix is an operating system based on Debian designed to be run directly from a CD / DVD (Live CD) or a USB key (Live USB), one of the first of its kind for any operating system. When starting a program, it is loaded from the removable medium and decompressed into a RAM drive.
Cooperative Linux (short-named coLinux) is the first working free and open source method for optimally running Linux on Microsoft Windows natively.
SpeedLinux is a customized coLinux. coLinux is not a VM but it can be used in the same way. Installation of Speedlinux results in a complete LINUX System with X server running side on side with Windows on a single PC.
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Portable Ubuntu Remix is a program which wrap an operating system and that runs inside Windows thanks to a compatibility layer; Knoppix is an operating system that can run inside Windows thanks to an emulator, but almost every operating system can run inside an emulator.