Virtualization

Operating-system-level virtualization, also known as containerization, refers to an operating system feature in which the kernel allows the existence of multiple isolated user-space instances.

The usual goal of virtualization is to centralize administrative tasks while improving scalability and overall hardware-resource utilization.

IBM added virtual memory hardware to the System/370 series in 1972 which is not the same as Intel VT-x Rings providing a higher privilege level for Hypervisor to properly control Virtual Machines requiring full access to Supervisor and Program or User modes.

Hardware-assisted virtualization was first introduced on the IBM 308X processors in 1980, with the Start Interpretive Execution (SIE) instruction.

IBM refers to its specific form of hardware virtualization as "logical partition", or more commonly as LPAR.

Paravirtualization improves performance and efficiency, compared to full virtualization, by having the guest operating system communicate with the hypervisor.

By allowing the guest operating system to indicate its intent to the hypervisor, each can cooperate to obtain better performance when running in a virtual machine.

However, even in cases where the operating system cannot be modified, components may be available that enable many of the significant performance advantages of paravirtualization.

This ensures run-mode compatibility across multiple encryption algorithm models, allowing seamless integration within the paravirtual framework.

Xen hypervisors based on any 2.6.24 or later kernel support pv-ops guests, as does VMware's Workstation product beginning with version 6.

[18] A hardware-assisted full virtualization approach uses an unmodified guest operating system that involves many VM traps producing high CPU overheads limiting scalability and the efficiency of server consolidation.

Since the resources are centralized, users moving between work locations can still access the same client environment with their applications and data.

[21] For IT administrators, this means a more centralized, efficient client environment that is easier to maintain and able to more quickly respond to the changing needs of the user and business.

[22] Another form, session virtualization, allows multiple users to connect and log into a shared but powerful computer over the network and use it simultaneously.

[20] With multiseat configuration, session virtualization can be accomplished using a single PC with multiple monitors, keyboards, and mice connected.

Thin clients, which are seen in desktop virtualization, are simple and/or cheap computers that are primarily designed to connect to the network.

They may lack significant hard disk storage space, RAM or even processing power, but many organizations are beginning to look at the cost benefits of eliminating "thick client" desktops that are packed with software (and require software licensing fees) and making more strategic investments.

[24] Operating-system-level virtualization, also known as containerization, refers to an operating system feature in which the kernel allows the existence of multiple isolated user-space instances.

This provides many of the benefits that virtual machines have such as standardization and scalability, while using less resources as the kernel is shared between containers.

With virtualization, several operating systems can be run in parallel on a single central processing unit (CPU).

This parallelism tends to reduce overhead costs and differs from multitasking, which involves running several programs on the same OS.

Using virtualization, an enterprise can better manage updates and rapid changes to the operating system and applications without disrupting the user. "