article Related Topics:
QEMU
 

QEMU is free software written by Fabrice Bellard that implements a fast processor emulator, allowing a user to run one operating system within another one. It is similar to projects such as Bochs, VMware Workstation and PearPC, but has several features these lack, including increased speed on x86, and support for multiple architectures in-progress. By using dynamic translation it achieves a reasonable speed while being easy to port on new host CPUs. QEMU has two operating modes:

User mode emulation
QEMU can launch Linux processes compiled for one CPU on another CPU. Linux system calls are converted because of endianness and 32/64 bit mismatches. Wine and Dosemu are the main targets for QEMU.
System mode emulation
QEMU emulates a full system, including a processor and various peripherals. It enables easier testing and debugging of system code. It can also be used to provide virtual hosting of several virtual PCs on a single server.

The majority of the program is under the LGPL, with the user mode emulation under the GPL.

Fabrice Bellard also wrote a closed source, currently free-of-charge, Linux kernel module (with preliminary ports to FreeBSD and Windows) named kqemu or QEMU Accelerator, which speeds up i386 emulation on i386 platforms to a level where the loss of speed is negligible even compared to native execution. This is accomplished by running user mode and virtual 8086 mode code directly on the host computer's CPU, and using processor and peripheral emulation only for kernel mode and real mode code. This is similar to what VMware Workstation and Virtual PC do. As a result, real mode DOS will not speed up much if at all as a guest OS, whereas Windows 2000 will run at close to native speeds. (Note, however, that as soon as a memory manager is used with DOS, most of DOS code is actually run in a virtual 8086 mode task, and should theoretically benefit from kqemu's speedup.)

Advantages of QEMU

  • Supports emulating IA-32 (x86) PCs, AMD64 PCs, MIPS R4000, Sun's SPARC sun4m, Sun's SPARC sun4u, ARM Integrator/CP board, SH4 SHIX board, ARM Versatile/AB board, and PowerPC (PReP and Power Macintosh) architectures.
  • Support for other architectures in both host and emulated systems (see homepage for complete list).
  • Increased speed — some applications can run in close to real time.
  • Implement Copy-On-Write disk image formats. You can declare a multi-gigabyte virtual drive, the disk image will only be as large as what is actually used.
  • Also implement overlay images. You can keep a snapshot of the guest system, and write changes to a separate image file. If the guest system breaks, it's simple to roll back to the snapshot.
  • Support for running Linux binaries for other architectures.
  • Can save and restore the state of the machine (programs running, etc.). Not made convenient yet, but possible.
  • Virtual network card emulation.
  • SMP support.
  • Guest OS does not need to be modified/patched
  • Performance is improved when the "free but closed sourced" kqemu kernel module is used, but not quite at the level of VMWare.
  • Command line tools allow a full control of Qemu without having to run X11.
  • Remote control of emulated machine via integrated VNC server
  • USB tablet support - this provides "grabless" mouse control. Activated with "-usb -usbdevice tablet".

Disadvantages of QEMU

  • Incomplete support for Microsoft Windows and other host operating systems (emulation of these systems is just fine).
  • Incomplete support for less frequently-used architectures.
  • No special device drivers (graphics, sound, IO) for guests are available thus quite large overhead for multimedia applications. It does emulate a Cirrus Logic graphics chip and several existing soundcards though, so using existing drivers for those does accomplish a similar task.

Example of QEMU's usage

This command will create a 500MB hard disk image in QEMU's "qcow" format qemu-img create -f qcow c.img 500M

In this command the -f option is for the disk image format. The following formats are supported: raw, qcow, cow, vmdk and cloop. See also: .img and .iso.

The following command will start a virtual machine with 128MB of memory, using the c.img file created with the previous command and booting from a CD-ROM image linux.iso. The virtual machine will have audio support and use the system's clock to run in "real time." Note that one could also replace the -cdrom linux.iso parameter with -cdrom /dev/cdrom or whatever one's CD-ROM device is, and physically boot from installation medium and install to the image specified after -hda, in this case c.img. qemu -hda c.img -cdrom linux.iso -boot d -m 128 -soundhw sb16 -localtime

This will create a virtual machine with 64MB of memory, booting from c.img and using the system's CD-ROM drive. The virtual machine will run in full-screen mode. qemu -hda c.img -cdrom /dev/cdrom -boot c -m 64 -full-screen

While a virtual machine is running, press Ctrl-Alt-2 to access the "QEMU console", which lets one control the virtual machine (for example, changing disk images, rebooting, quitting QEMU, etc.) and Ctrl-Alt-1 to switch back to your emulation. Ctrl-Alt-F toggles between full-screen and windowed mode.

kqemu versus QVM86

Fabrice Bellard has stated his willingness to open-source the kqemu QEMU Accelerator module if a company steps up to sponsor it. This has so far not happened, and kqemu remains proprietary. It is free to use, but one is not allowed to distribute it to other people without an explicit authorisation. Distributors wishing to include the QEMU accelerator on CDs, ISO images or packages must contact the author to know the exact terms.

Meanwhile, a GPL licensed module purporting to perform the same task, QVM86, has appeared, although as of early 2006, it appears to be unmaintained.

kqemu has been licensed by Win4Lin for use in their Win4Lin Pro Desktop product.

See also

External links

PowerPC emulators | x86 emulators | Mac OS emulation software | Linux emulation software | Windows emulation software | Virtualization software

QEMU | QEMU | QEMU | QEMU | QEMU | QEMU | Qemu | QEMU

 

This article is licensed under the GNU Free Documentation License. It uses material from the "QEMU".

Home Page • arts • business • computers • games • health • hospitals • home • kids & teens • news • physicians • recreation• reference • regional • science • shopping • society • sports • world