Overview of virtualization technologies

Technologies

Hardware emulation

In hardware emulation, all hardware components (CPU, chipset, I/O cards, etc.) are emulated. The CPU emulation translates hardware instructions from the emulated to the native CPU (for example emulation of PowerPC, ARM, SPARC, MIPS, ... on x86). This results in significant overhead and, consequently, a loss of performance.

Guest operation systems can be operated without adjustments.

Examples for hardware emulation:

• Bochs
• QEMU
• PearPC
• Windows Virtual PC for Mac (PPC) (no longer supported)

Hardware virtualization

Similar to hardware emulation, numerous hardware components are emulated (chipset, I/O cards,...) However, the CPU is not emulated, but some CPU instructions are intercepted and adjusted. Therefore, only the CPU architecture can be used in the guest systems, which is also available physically in the host systems. However, performance is significantly higher than with hardware emulation.

Guest operating systems can be operated without adjustments.

Examples for hardware virtualization:

• VMware vSphere 5.5, VMware Workstation
• Microsoft Hyper-V
• VirtualBox
• XEN starting with version 3 and using Hardware Virtual Machine (HVM), requires an Intel VT/AMD-V CPU

Paravirtualization

In paravirtualization, no hardware emulation takes place. The host offers instead a special API for hardware access. In the guest systems, only the CPU architecture can be used that is also available in the host system physically.

Guest systems (kernel) must be adapted, but the ABI (Application Binary Interface) remains unchanged.

Example:

• XEN
• VMware vSphere (paravirtualized device drivers, and previously also paravirtualized CPUs with VMI)

Operating system virtualization / container

There is also no emulation. There is only one kernel for host and guest system. Therefore, the guest operating system can only be the same operating system as the one running on the host (for example Linux on Linux, different distributions are possible). This technology has a low overhead, as no emulation takes place and syscalls pass through only one kernel, not two. Guest systems can be started within seconds.

Examples:

• Linux Containers LXC
• OpenVZ
• Linux-VServer
• Solaris Containers
• FreeBSD Jails

More information

• Virtualisierung (Informatik) (de.wikipedia.org)
• Wann lohnt sich Virtualisierung für kleine und mittelständische Unternehmen? (tecchannel.de, 13.01.2015)

References

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Author: Florian Hettenbach

Translator: Alina Ranzinger Alina has been working at Thomas-Krenn.AG since 2024. After her training as multilingual business assistant, she got her job as assistant of the Product Management and is responsible for the translation of texts and for the organisation of the department.