Running Linux, 5th Edition - Matthias Kalle Dalheimer [494]
The files on the parent of a linked clone continue to exist at the time one creates a snapshot, and continue to remain available to the linked clone. Changes to the parent don't affect the linked clone, and changes to the disk of the linked clone don't affect the parent.
Other Programs for Running MS-DOS and Windows Applications on Linux
A number of other attempts have been made by different groups of developers, both open source and commercial, to bring DOS and Windows programs to Linux. The simplest is Dosemu (http://www.dosemu.org), which emulates PC hardware well enough for MS-DOS (or compatible systems such as PC-DOS or DR-DOS) to run. It is still necessary to install DOS in the emulator, but since DOS is actually running inside the emulator, good application compatibility is assured. To a limited extent, it is even possible to run Windows 3.1.
Another open source project is Bochs (http://bochs.sf.net), which emulates PC hardware well enough for it to run Windows and other operating systems. However, because every 386 instruction is emulated in software, performance is reduced to a small percentage of what it would be if the operating system were running directly on the same hardware.
The plex86 project (http://savannah.nongnu.org/projects/plex86) takes yet another approach, and implements a virtualized environment in which Windows or other operating systems (and their applications) can run. Software running in the virtual machine runs at full speed, except for when it attempts to access the hardware. It is very much like Dosemu, except the implementation is much more robust, and not limited to running just DOS.
At the time this book was written, all of the projects discussed so far in this section were fairly immature, and significantly limited. To put it bluntly, the sayings, "Your mileage may vary" and "You get what you pay for" go a long way here.
You may have better luck with a commercial product, such as VMware (http://www.vmware.com) or Win4Lin (http://www.win4lin.com). Both of these work by implementing a virtual machine environment (in the same manner as plex86), so you will need to install a copy of Windows before you can run Windows applications. The good news is that with VMware, at least, the degree of compatibility is very high. VMware supports versions of DOS/Windows ranging from MS-DOS to .NET, including every version in between. You can even install some of the more popular Linux distributions, to run more than one copy of Linux on the same computer. To varying extents, other operating systems, including FreeBSD, NetWare, and Solaris, can also be run. Although there is some overhead involved, modern multi-gigahertz CPUs are able to yield acceptable performance levels for most common applications, such as office automation software.
Win4Lin is a more recent release than VMware. At the time of this writing, it ran Windows and applications faster than VMware, but was able to support only Windows 95/98/ME, and not Windows NT/2000/XP. As with other projects described in this section, we suggest keeping up-to-date with the product's development, and check once in a while to see if it is mature enough to meet your needs.
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[*] Xen, which is free software, is another, increasingly popular virtualization tool that allows a large computer server to host multiple versions of Linux and some other operating systems.
Remote Desktop Access to Windows Programs
In this section of the chapter, we switch gears and look at Linux as a thin client for a Microsoft Windows terminal server. Under this scenario, a site's system administrator runs the applications desired by the users on a central Windows system (making sure there are enough licenses to support all the users), and the users access the application transparently through Linux systems. Performance is often better than when users run the