Comparison of virtual machines

The table below compares basic information about virtual machine (VM) packages. Note that these are all virtual machines in the 'hypervisor' or 'hardware emulator' sense. None of them are VMs in the Application Virtualization sense as the Java Virtual Machine or Parrot virtual machine. For those, see Comparison of Application Virtual Machines.

• ^  Providing any virtual environment usually requires some overhead of some type or another. Native usually means that the virtualization technique does not do any CPU level virtualization (like Bochs), which executes code more slowly than when it is directly executed by a CPU. Some other products such as VMWare and Virtual PC use similar approaches to Bochs and QEMU, however they use a number of advanced techniques to shortcut most of the calls directly to the CPU (similar to the process that JIT compiler uses) to bring the speed to near native in most cases. However, some products such as coLinux, Xen, z/VM (in real mode) do not suffer the cost of cpu level slow downs as the cpu level instructions are not proxied or executing against an emulated architecture since the guest OS or hardware is providing the environment for the applications to run under. However access to many of the other resources on the system, such as devices and memory may be proxied or emulated in order to broker those shared services out to all the guests, which may cause some slow downs as compared to running outside of virtualization.
• ^  OS-level virtualization is described as "native" speed, however some groups have found overhead as high as 3% for some operations, but generally figures come under 1%, so long as secondary effects do not appear.
• ^  See [22] for a paper comparing performance of paravirtualization approaches (eg Xen) with OS-level virtualization
• ^  Requires patches/recompiling.
• ^  Very good for light-weight, paravirtualized single-user VM/CMS interactive shell: largest customers ran several thousand users on single system. Highly variable for multiprogramming OSes like Linux on zSeries, z/OS that make heavy use of native supervisor state intructions, depending on nature of workload.

Features

The table below compares features of virtual machine packages.

• ^  VirtualBox User Manual, Chapter 9.9; requires usage of VBoxManage internalcommands createrawvmdk which says:This is a development tool and shall only be used to analyse problems. It is completely unsupported and will change in incompatible ways without warning.

Other emulators

Other (free, maintained) emulators not mentioned above:

SkyEye 1.2.1

• http://www.skyeye.org/
• http://sourceforge.net/projects/skyeye/
• http://gro.clinux.org/

SkyEye is an Open Source Simulator, which simulates series ARM architecture based microprocessors and Blackfin DSP Processor. Users can run Operating Systems such as Linux, uCLinux, uC/OS-II for ARM and can analyze or debug in source level.
http://sourceforge.net/project/showfiles.php?group_id=85554

PearColator

• http://pearcolator.wiki.sourceforge.net/

PearColator is a development Open Source binary translator that can take x86, PowerPC and ARM machine codes and compile them using a high performance JVM's JIT compiler to run on PowerPC and Intel architectures. It is unusual in that it is being written in Java using the same compiler to optimize itself as the emulated architectures.

References

External links

• Technical comparison of Linux virtualization technologies.