QEMU (Quick Emulator) is an open-source emulator and virtualization tool that supports multiple architectures and hardware platforms.It can emulate an entire computer system, including the processor, memory, storage devices, and various peripherals.

History and Evolution

QEMU was initially designed as an emulator that could simulate computer systems with different architectures. Later, it evolved into a powerful virtualization tool capable of running virtual machines on different host systems, such as Linux, Windows, and macOS.

QEMU offers high flexibility and customization, allowing users to configure and manage virtual machines in a fine-grained manner. It can operate in environments without hardware virtualization, enabling scenarios such as running the X system ona virtual machine or running an ARM system on an x86 machine.

Applications

QEMU is widely used in various fields, including:

• Development and testing
• Embedded systems
• Cloud computing

Running Modes

QEMU primarily operates in two different modes:

Hardware-Assisted Mode

This mode leverages hardware virtualization extensions, such as Intel VT-x or AMD-V, to provide virtualization capabilities. It offers better performance and compatibility with specific hardware components.

System Emulation Mode

This mode does not rely on hardware virtualization and instead emulates the entire hardware system, including the processor and peripherals. It allows QEMU to run on a wider range of host systems but may result in lower performance.

Virtual Machine Disk Formats

QEMU supports various virtual machine disk formats, each with its own characteristics and advantages:

• Qcow2 (QEMU Copy On Write 2): A widely used format that supports snapshotting, dynamic space allocation (thin provisioning), and compression.
• VMDK (Virtual Machine Disk): The standard disk format for VMware virtual machines. QEMU can read and convert VMDK disk images.
• VHD (Virtual Hard Disk): The disk format used by Microsoft Hyper-V and VirtualBox. QEMU can also read and convert VHD disk images.
• RAW (Raw Image): A raw disk image format that does not undergo any compression or special processing. QEMU can directly read RAW image files.
• QCOW (QEMU Copy On Write): An older disk format used by early versions of QEMU, now superseded by Qcow2. However, QEMU can still handle disk images in this format.

QEMU can also work with or convert to other formats, such as VDI (VirtualBox Disk Image), IMG, and ISO.

Emulating a Virtual Machine Within a Virtual Machine

QEMU's versatility allows it to run multiple layers of virtualization. For example, one can create a virtual machine on a host system and then use QEMU within that virtual machine to run another virtual machine.

This technique is often used in situations where hardware interaction is not essential, such as embedded systems development, where developers can simulate the behavior of embedded systems directly on their host systems.

Conclusion

QEMU is a powerful and flexible tool that enables users to create and manage virtual machines for various purposes. Its support for multiple architectures, operating systems, and disk formats makes it a versatile solution for developers, testers, and researchers.

Whether you are looking to emulate a legacy system, run multiple operating systems simultaneously, or develop embedded software, QEMU provides a comprehensive and effective solution.

哪家公有云支持嵌套虚拟化

Azure。 Azure新一代的机器支持嵌套虚拟化，使问题有了更好的解决方法。 嵌套虚拟化就是在基于宿主机A搭建的虚拟机B上再跑一个虚拟机C，主要问题在于，虚拟机B是否支持硬件虚拟化，否则KVM无法启用。

在虚拟机里还能再装虚拟机吗?

可以的，不过你的虚拟机要开启“虚拟化引擎”中的“虚拟化”功能，如果你的物理机器性能不是很好，不建议在虚拟机里安装虚拟机，因为那样体验会比较差。 楼主是想用虚拟机安装Linux系统用来学习吗？如果是的话，可以网络《Linux就该这么学》，里面有具体讲解如何用虚拟机安装Linux系统，只要照着书本一步步操作就可以了。