Virtual machine

A computer can act like a new one.

It can run a whole other system inside. We call the real computer the host. The fake computer is the guest.

A guest can run its own tools. One host can have many guests. This lets you run different systems at once. It is like having many computers in one. You can even try new software safely. This is a great way to learn.

A computer can act like a new one. This is called a virtual machine.

It uses software to mimic a real computer system. We call the real computer the host. The fake computer is called the guest.

One host can run many guests at once. This helps people run different systems on one machine. You can run Windows and Linux at the same time. This is useful for testing new software safely. It is like a sandbox for programs.

There are different kinds of virtual machines. A system virtual machine acts like a whole computer. It uses a hypervisor to manage the hardware. A hypervisor is a tool that shares the host's parts. This keeps each guest isolated from the others. There are also process virtual machines. These run as a normal app inside the host. They help a program run the same way on any computer. The Java virtual machine is a famous example. This makes it easy to write code for many different machines.

Some systems even use special hardware to help them work faster.

A virtual machine is a way to make a computer act like another computer system.

It uses software or special hardware to imitate a real machine. This process is called virtualization. We call the real, physical computer the "host." The virtual computer running inside it is called the "guest."

One host can run many different guests at the same time. This is very useful for running different operating systems together. For example, you could run Windows and Linux on one machine. This helps people test new software in a safe place called a sandbox.

There are different ways these machines work. A system virtual machine acts like a whole computer. It uses a tool called a hypervisor to manage the hardware. The hypervisor shares the host's parts so many guests can exist at once. Each guest stays isolated from the others. Modern hypervisors often use hardware-assisted virtualization to work better. This means the computer's brain, or CPU, has special features to help the hypervisor.

Another type is a process virtual machine. This type runs as a normal application inside the host. It is created when a program starts and disappears when it closes.

Process virtual machines help programs run on any computer. They hide the tricky details of the hardware from the software. This makes it easier for programmers to write code that works everywhere. The Java virtual machine is a very famous example of this. Other examples include the .NET Framework and the Parrot virtual machine. Some special versions even help large groups of computers work together as one cluster. These systems let programmers focus on their ideas instead of how machines talk to each other.

People have been working on these ideas since the 1960s. System virtual machines grew from a method called time-sharing. This let many people use one computer at the same time. IBM created important early systems like the CP-40 and the CP-67. These were some of the first to use full virtualization. Process virtual machines also started around the same time. In 1966, the O-code machine was used to help move code to new systems. Later, the Pascal-P system used something called p-code in the 1970s.

Virtual machines are part of our digital world every day. They help servers work more efficiently through server consolidation. This means many tasks can live on one strong machine. They are also great for making new software. Developers can use them to find mistakes or reboot systems very quickly.

You might even use them if you like old video games. Some emulators let you play games designed for older consoles on a modern computer. Whether for work or play, these digital mimics are very powerful tools.

A virtual machine (VM) is the virtualization or emulation of a computer system. In simple terms, it is a software-based version of a physical computer. These machines are built on computer architectures to provide the same functionality as real hardware. They can be created using specialized hardware, software, or a combination of both.

By using a VM, a single physical computer can act like many different machines at once. This allows for much greater flexibility in how we use computing power.

To understand how this works, we must distinguish between the "host" and the "guest." The physical, real-world hardware running the system is called the host. The virtual machine running on that hardware is called the guest.

A single host can run several guests simultaneously. Each guest can run its own unique operating system, such as Windows or Linux. This is possible because the host manages the hardware to create isolated environments for each guest.

System virtual machines, also known as full virtualization VMs, provide a complete substitute for a real machine. These machines allow an entire operating system to execute within the virtual environment. A hypervisor is the key tool used here; it manages and shares the host's hardware resources. Modern hypervisors often use hardware-assisted virtualization. This means the host's central processing unit (CPU) has specific hardware features designed to help the hypervisor run guests more efficiently.

Another type is OS-level virtualization, where the computer's kernel partitions its resources.

Process virtual machines, or application virtual machines, work differently. Instead of simulating a whole computer, they run as a normal application inside a host operating system. A process VM is created when a specific program starts and is deleted when that program closes. Its main goal is to provide a platform-independent environment. This means a programmer can write code that runs the same way on any device, regardless of the underlying hardware. The Java virtual machine (JVM) is a famous example of this technology. Other examples include the .NET Framework and the Parrot virtual machine.

The history of these technologies dates back to the 1960s. System virtual machines grew out of a concept called time-sharing. This allowed multiple users to use one computer at the same time by switching between programs in small time slices. IBM was a leader in this field with research systems like the CP-40 and CP-67, which provided early examples of full virtualization. Process virtual machines also emerged around 1964. An early example was the META II compiler-writing system. Later, the Pascal-P system in the 1970s used "p-code," a method that influenced many modern interpreters like the Java virtual machine.

Virtual machines offer many practical advantages for modern computing. One major use is server consolidation, where many virtual machines run on one strong physical machine to save resources. They are also used as "sandboxes" for testing unproven or novel software. If the software fails, it only affects the guest, not the host. Developers also use them for better debugging access and faster reboots. In embedded systems, a VM might allow a real-time operating system to run alongside a complex one like Linux.

There are even specialized process VMs designed for computer clusters. Instead of a single process, these systems use one process per physical machine in a group. They help programmers manage concurrent applications by handling the communication between machines. This allows the programmer to focus on algorithms rather than the complex details of how machines talk to each other. Examples include the Parallel Virtual Machine (PVM) and the Message Passing Interface (MPI). Whether used for massive server farms or running a single application, virtual machines remain a fundamental part of computer science.