I am really new to virtualization , i have read in some places that hardware virtualization is also referred as hardware assisted virtualization , is it true or false.
From my understanding hardware virtualization means Hardware itself has some embedded software which is helpful in managing systems resources between OS , is it right.
And if possible tell me what are the different types of Virtualization?
Different types of virtualization
In the traditional x86 architecture, operating system kernels expect direct CPU access running in Ring 0, which is the most privileged level.
Software Virtualization
With software virtualization, guest operating systems cannot run in Ring 0 because the VMM sits there. The guest operating systems must therefore run in Ring 1, but there's a catch: Some x86 instructions work only in Ring 0, so the operating systems must be recompiled to avoid them. This process is called paravirtualization, and it is impractical — especially if the source code for the OS is not available. To get around this, VMMs traps these instructions and emulates them, which unfortunately results in an enormous performance hit: Virtual machines can be significantly slower than real physical ones.
Hardware Assisted Virtualization
Thus, Intel and AMD have introduced their new virtualization technologies, a handful of new instructions and — crucially — a new privilege level. The hypervisor can now run at "Ring -1"; so the guest operating systems can run in Ring 0. There's no need for paravirtualization, the VMM does less work, and the performance hit is reduced
Wiki puts it very nicely
Virtualization
The term "virtualization" was coined in the 1960s to refer to a virtual machine (sometimes called "pseudo machine"), a term which itself dates from the experimental IBM M44/44X system. The creation and management of virtual machines has been called "platform virtualization", or "server virtualization", more recently.
Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine (VM), for its guest software. The guest software is not limited to user applications; many hosts allow the execution of complete operating systems. The guest software executes as if it were running directly on the physical hardware, with several notable caveats. Access to physical system resources (such as the network access, display, keyboard, and disk storage) is generally managed at a more restrictive level than the host processor and system-memory. Guests are often restricted from accessing specific peripheral devices, or may be limited to a subset of the device's native capabilities, depending on the hardware access policy implemented by the virtualization host.
Hardware-assisted virtualization In hardware-assisted virtualization, the hardware provides architectural support that facilitates building a virtual machine monitor and allows guest OSes to be run in isolation. Hardware-assisted virtualization was first introduced on the IBM System/370 in 1972, for use with VM/370, the first virtual machine operating system. In 2005 and 2006, Intel and AMD provided additional hardware to support virtualization. Sun Microsystems (now Oracle Corporation) added similar features in their UltraSPARC T-Series processors in 2005. Examples of virtualization platforms adapted to such hardware include Linux KVM, VMware Workstation, VMware Fusion, Microsoft Hyper-V, Microsoft Virtual PC, Xen, Parallels Desktop for Mac, Oracle VM Server for SPARC, VirtualBox and Parallels Workstation.
Also refer to the following links for more explanations: http://searchvmware.techtarget.com/definition/hardware-virtualization http://www.anandtech.com/show/2480
