What Is a Virtual Machine? Host, Guest, and Hypervisor Basics
Learn what a virtual machine is, how host and guest operating systems interact, how VMware Player works as a Type 2 hypervisor, and how to plan VM resources.
A virtual machine (VM) is a software-created computer environment. It can boot an operating system, run applications, store files, and connect to networks much like a separate physical computer. The difference is that its computer hardware is represented in software and backed by resources from a real computer.
The virtual machine is not the same thing as the application that runs it. The VM is the virtual computer and its configuration and storage files. VMware Player is the virtualization software used to create, open, configure, and run that VM.
Host, Guest, and Physical Machine
The physical machine is the actual computer containing the processor, memory, storage, network hardware, and other devices. The host system is that physical computer when it is running virtualization software.
The host operating system is the operating system installed directly on the physical computer. For example, Windows can be the host operating system on a laptop. VMware Player runs within that host operating system as a desktop application.
The guest operating system is the operating system installed inside a virtual machine. A Windows host can run a Linux guest, for example. The guest is installed, started, updated, configured, and administered separately from Windows.
| Aspect | Host operating system | Guest operating system |
|---|---|---|
| Where it runs | Directly on the physical computer | Inside a virtual machine |
| Relationship to physical hardware | Controls the computer and supplies resources to applications, including VMware Player | Uses virtual devices presented by the hypervisor |
| How it is installed | Installed on the physical computer | Installed in a VM from an ISO image or physical optical media |
| Who manages it | Managed as the main computer operating system | Managed independently inside the VM |
| Effect when the host shuts down | The host stops or restarts | Running guests are also stopped, suspended, or interrupted depending on the action |
| Examples | Windows or Linux installed on the physical computer | Linux running in a VM on Windows, or another supported combination |
Virtual Hardware Inside a VM
A guest operating system expects to find familiar computer devices. VMware Player presents software-defined devices so the guest can use a virtual computer.
- Virtual CPU (vCPU): processor capacity presented to the guest.
- Virtual memory: a configured portion of the host's RAM made available to the guest while the VM runs.
- Virtual disk: a file or set of files that represents the VM's storage. The guest treats it like a hard disk.
- Virtual network adapter: a software network device through which the guest communicates with the host, other computers, or the internet according to the selected networking configuration.
- Virtual optical drive: a software CD/DVD device that can connect to an ISO image or physical optical media.
The guest operating system sees these devices as its computer hardware. However, the devices are backed by the physical computer. A virtual disk consumes host storage, virtual memory uses host RAM, and vCPUs require host processor capacity.
| Host resource | Virtual device presented to guest | Planning consideration |
|---|---|---|
| Processor | Virtual CPU | Assign enough processing capacity for the guest, but leave sufficient CPU capacity for the host and other applications. |
| Memory | Virtual memory | The assigned amount is taken from available host RAM while the VM is powered on. |
| Storage | Virtual disk | The virtual disk is stored as files on the host and requires adequate free space. |
| Network connection | Virtual network adapter | Connectivity depends on the chosen networking mode and the host's physical network. |
| Optical installation media | Virtual optical drive | Connect a valid ISO image or physical disc when installing the guest OS. |
VM hardware settings commonly include the guest operating system type, vCPU count, memory allocation, virtual disk, network adapter, and virtual CD/DVD device. These settings can be reviewed and adjusted through the virtualization application, subject to compatibility and resource limits.
What Is a Hypervisor?
A hypervisor is the virtualization layer that creates and runs virtual machines. It presents virtual devices to guests and coordinates their access to physical CPU, RAM, storage, networking, and other hardware.
At a conceptual level, resource allocation works like this: the VM receives a configured set of virtual resources, while the host supplies the underlying physical capacity. The hypervisor schedules and manages access so that the guest can operate without directly controlling the physical hardware.
This separation helps keep the guest environment distinct from the host. A guest does not automatically receive unrestricted access to host files, removable devices, or other hardware. File sharing, device connection, and networking features must be intentionally configured and must have suitable permissions.
VMware Player as a Type 2 Hypervisor
VMware Player operates as a hosted, or Type 2 hypervisor. A Type 2 hypervisor runs as an application within a conventional host operating system. Therefore, VMware Player must be installed on a supported host operating system; it is not installed directly on bare physical hardware as the primary system layer.
A Type 1 hypervisor runs more directly on server hardware or within a dedicated virtualization layer. That broad model is common in server environments. VMware Player instead uses the desktop-oriented Type 2 arrangement shown below.
| Layer | Purpose | Example |
|---|---|---|
| Physical hardware | Provides actual processing, memory, storage, and connectivity | A desktop or laptop computer |
| Host operating system | Controls the physical computer and runs ordinary applications | Windows |
| VMware Player / Type 2 hypervisor | Creates, configures, and runs VMs while coordinating hardware access | VMware Player |
| Virtual machine hardware | Provides software-presented devices to the guest | vCPU, virtual memory, virtual disk, and virtual network adapter |
| Guest operating system | Runs inside the VM and uses its virtual devices | Linux |
| Guest applications | Run within the guest OS | A Linux text editor or development tool |
In this example, the complete order is: physical hardware → host operating system → VMware Player → virtual machine hardware → guest operating system → guest applications.
How the Host and Guest Work Together
When a VM is powered on, it consumes host resources. VMware Player requests processor time, RAM, storage access, and networking services from the host. The host continues running its own applications, so both the host and guest compete for the physical computer's capacity.
The guest behaves as an independent operating system for normal tasks. It has its own users, files, settings, installed applications, updates, and shutdown process. Nevertheless, it remains dependent on the host and hypervisor. If the host is shut down or restarted, running guests are affected because their underlying computer has stopped or restarted.
Host and guest environments are separate by default. A file saved in the host's documents folder does not automatically appear in the guest, and a USB device does not automatically become available to both systems. Shared folders, removable-device connections, copy and paste, and networking are integration features that require deliberate configuration.
Benefits of Virtual Machines
- Portability: a VM can commonly be moved or copied as a set of virtual-machine files. Compatibility, hardware configuration, software versions, and operating-system or application licensing still need to be considered.
- Manageability: virtual hardware settings can be reviewed and adjusted through VMware Player without physically installing new components.
- Isolation: guest software is separated from the host and other guests by default, reducing direct interaction. Isolation is useful but is not an absolute security boundary.
- Learning and testing: users can explore another operating system or test software without replacing the host OS or repartitioning the physical computer.
For example, a learner can install VMware Player on a Windows computer, create a VM, attach a Linux ISO image, and explore Linux while Windows remains the host operating system.
Basic Workflow for Using a VM
- Install VMware Player on the host operating system. See Install VMware Player on Windows or Install VMware Player on Linux.
- Create or open a virtual machine. The general creation process is covered in Create a Virtual Machine.
- Choose the guest operating system type and assign virtual hardware such as vCPUs, memory, disk capacity, and networking.
- Attach an ISO image or other installation media to the VM's virtual CD/DVD device. An ISO image is a disk-image file commonly used as virtual installation media.
- Power on the VM and complete the operating-system installer inside the guest. For a manual process, see Manually Install a Guest Operating System.
- Remove or disconnect the installation media after installation if the VM tries to start the installer again.
- Start the guest and install applications inside it. Those applications, their files, settings, and updates belong to the guest environment rather than being ordinary host applications.
Resource Planning and Limitations
Virtualization does not create unlimited CPU, memory, disk, or network capacity. Every virtual resource ultimately depends on a physical resource in the host computer.
Assigning too much RAM can leave the host short of memory. Assigning too many vCPUs can increase contention and reduce responsiveness rather than making the guest faster. A practical starting point is to give the guest only the resources its operating system and applications need, while reserving enough capacity for the host and normal host applications.
Guest performance depends on the host's processor, RAM, storage speed, and network connection; the host's current workload; the VM configuration; and the guest operating system's own requirements. Operating-system licenses and application compatibility also continue to apply inside a VM.
For example, on a computer with limited RAM, assign the guest a modest amount so Windows and VMware Player retain enough memory for normal operation. If the host begins using extensive disk-based memory, both systems may become slow.
Troubleshooting Common Beginner Problems
The VM is slow and the host becomes unresponsive
- The guest may have been assigned too much memory or too many processor resources.
- The host may lack sufficient free RAM, CPU capacity, or disk performance.
- Reduce the VM allocation, close unnecessary host applications, and verify that the computer can support both operating systems.
For memory-specific configuration, see Change the Memory Allocation.
The operating-system installer does not start
- Check that an ISO image or installation disc is attached to the virtual CD/DVD device.
- Confirm that the ISO is valid and bootable.
- Make sure the virtual optical device is connected when the VM powers on and that the boot device configuration is appropriate.
The virtual optical device is discussed in Add a CD-ROM Drive.
Host files or devices do not appear automatically in the guest
- Host and guest are separate environments by default.
- File sharing, removable-device access, or networking may not have been configured.
- Enable the required integration feature deliberately and check permissions. See Shared Folders Overview and Connect a USB Device to a Virtual Machine.
VMware Player cannot be installed inside a guest as the physical host layer
This usually indicates confusion between the host OS, the hypervisor application, and the guest OS. VMware Player is a Type 2 hypervisor, so it requires an existing supported host operating system. Review the layer order: physical hardware, host OS, VMware Player, VM, and guest OS.
Key Terms to Remember
- Virtual machine: a software-defined computer that runs an operating system and applications in a virtual environment.
- Host system: the physical computer on which virtualization software and VMs run.
- Host operating system: the OS installed directly on the physical computer.
- Guest operating system: the OS installed and run inside a VM.
- Hypervisor: software or firmware that creates VMs and manages their use of physical hardware.
- Type 2 hypervisor: a hosted hypervisor that runs as an application inside a conventional host OS.
- Virtual hardware: software-presented devices used by a guest OS.
- Virtual disk: a file or group of files representing VM storage. See What Is a Virtual Disk.
- ISO image: a disk-image file commonly used as guest installation media.
- Isolation: separation between a guest environment and the host or other guests, reducing direct interaction by default.