Virtual Memory | Virtual OS | Virtual Desktop | Virtual Machine | Virtual Server

Virtual Memory

Virtual memory is the use of space on a hard disk drive (HDD) to simulate additional main memory.

An imaginary memory area supported by some operating systems (for example, Windows but not DOS) in conjunction with the hardware. You can think of virtual memory as an alternate set of memory addresses. Programs use these virtual addresses rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses are converted into real memory addresses.

Virtual OS

An operating system that can host other operating systems.

Guest OS

A guest OS is an operating system that is installed in a virtual machine or disk partition in addition to the host or main OS.

In virtualization, a single computer can run more than one OS at the same time. In disk partitioning, a guest OS must be the same as the host OS. In a virtualization solution, a guest OS can be different from the host OS. A program called Boot Camp allows users of Intel-based Macintosh (Mac) computers to run Windows XP as the guest OS. Once Boot Camp has been installed on the Mac's hard disk, the user can boot the computer using either Mac OS X or Windows XP.

Virtual Desktop

A virtual desktop is an individual user's interface in a virtualized environment.

The virtualized desktop is stored on a remote server rather than locally. Desktop virtualization software separates the physical machine from the software and presents an isolated operating system for users.  Desktop virtualization tools include Microsoft Virtual PC, VMware Workstation and Parallels Desktop for Mac.

Virtual Machine

A virtual machine (VM) is a "completely isolated operating system installation within your normal operating system".

A virtual machine is a tightly isolated software container that can run its own operating systems and applications as if it were a physical computer. A virtual machine behaves exactly like a physical computer and contains it own virtual (ie, software-based) CPU, RAM hard disk and network interface card (NIC). 

Virtual Infrastructure

A virtual infrastructure lets you share your physical resources of multiple machines across your entire infrastructure. 

A virtual machine lets you share the resources of a single physical computer across multiple virtual machines for maximum efficiency. Resources are shared across multiple virtual machines and applications. Your business needs are the driving force behind dynamically mapping the physical resources of your infrastructure to applications—even as those needs evolve and change. Aggregate your x86 servers along with network and storage into a unified pool of IT resources that can be utilized by the applications when and where they’re needed. This resource optimization drives greater flexibility in the organization and results in lower capital and operational costs.

Virtual Server

A server, usually a Web server, that shares computer resources with other virtual servers. In this context, the virtual part simply means that it is not a dedicated server -- that is, the entire computer is not dedicated to running the server software.

Virtual Web servers are a very popular way of providing low-cost web hosting services. Instead of requiring a separate computer for each server, dozens of virtual servers can co-reside on the same computer. In most cases, performance is not affected and each web site behaves as if it is being served by a dedicated server. However, if too many virtual servers reside on the same computer, or if one virtual server starts hogging resources, Web pages will be delivered more slowly.