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7.1 Virtual machines


This has been available for mainframes for a while now. You can boot several different OS at once on the same server. This is mainly used to isolate environments. For example, you can install the new version of an OS on the same server, even while the server is running the current version. This allows you to test and do a roll-out gracefully.

The advantages of virtual machines are:

  • Total flexibility. You can run many different OS and different version of the same OS, all at once.
  • Robustness. You have total isolation. One OS may crash without affecting the other.
  • Resource management. You can effectively limit the resources taken by one OS.
  • Hardware Independence. The client OS is using virtual disks provided by the host OS.

This technology is not directly available on PCs. The Intel x86 architecture does not support visualization natively. Some products nevertheless have appeared and provide this. You can run Linux inside Linux, or this other OS (Which BTW has a logo showing a window flying in pieces, which quite frankly tells everything about it).

The solutions available on PCs carry most of the advantages of the virtual machines found on mainframe, except for performance. You can't run that many virtual Linux's using this technology and expect it to fly. One example of this technology is vmware, which is quite useful, especially if you must run this other OS... vmware may be used to run Linux inside Linux, even test Linux installation while running linux...

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