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How do virtual desktops work?
Virtual desktops and the underlying virtual machines are a critical part of many organization's end-user technology stacks, so admins need to understand the basics of how they work.
Virtual desktops have been a fundamental and powerful resource for IT professionals and computer hobbyists since the Windows 2000 days and are still widely popular.
With virtual desktops, multiple desktops run on a single physical computer in a virtual network. IT teams can use them to test new apps, updates, and patches in addition to deploying them as production desktops that can go out to bulk end users.
Their flexibility can sometimes be confusing, especially with each vendor's virtual machine (VM) software operating a bit differently, so it's important for administrators to understand the basics of how virtual desktop technology works.
How do virtual desktops and virtual machines work?
Fundamental to the function of virtual desktops is the underlying VM that hosts it. The virtual desktop or virtual desktops run on the VMs based on parameters that administrators set for them. These parameters include the OS, relevant software and the allocation of physical resources such as disk space, CPU, memory and network interfaces.
Figure 1 shows Microsoft's Hyper-V manager running on a Windows 10 Laptop, displaying a VM with Windows 10 loaded on it. Virtualization technology in this context has been very popular with corporate IT staff for decades to test new applications, upgrades and patches without spending precious budget funds on additional hardware. It functions well as a laboratory environment.
VM clients and servers appear as software representations of physical machines. If an application crashes the VM, or a new OS update causes the VM to fail to boot, admins can instantly restore the VM from a previous checkpoint or simply deleted and re-create the session. The physical machine is unaffected.
SMBs and enterprise organizations alike can take advantage of VM technology because there are numerous free versions of products on the market in addition to the paid, more feature-rich versions. The free versions are typically limited in scalability, management features, support and advanced features, such as custom APIs, but the vendors will gladly provide an upgrade to a more powerful version for a price. The more popular VM software products include the following:
- Oracle VirtualBox. A free, open source product that supports Linux, macOS and Windows.
- VMWare Workstation Pro. One of the first VM products widely available, it moved from a subscription model to free for personal use. Paid subscriptions and support are currently not available. This is intended for home users; it supports Windows, Linux and other OSes in the VM. SMBs can use Workstation Pro for small-scale testing and training.
- Microsoft Developer. With a free account, admins can use this service and its VM software, including the latest versions of Windows, developer tools, SDK, samples and more. This is advantageous for Windows developers who want to experiment with VMs.
- Citrix Hypervisor. There is a free edition, but it has limited features. Citrix customers can download the software from the Citrix downloads site.
- VMWare ESXi (vSphere) and GSX. This service offers a free version for small businesses and individuals. VMWare ESXi is a bare-metal OS similar to Hyper-V Server, while VMWare GSX uses a client-server model similar to Hyper-V Manager.
- Microsoft Hyper-V Manager. This is a powerful tool that is free and built into Windows 10 and Windows 11. This allows admins to create and manage VMs and install any OS -- Windows client, Windows Server, even Windows Server Core. This should not be confused with Hyper-V Server, which is a Server Core installation with Hyper-V enabled. Hyper-V Server is a stand-alone product, popular for complex virtualization configurations for data centers and hybrid cloud environments.
Azure Stack HCI is Microsoft's new product that will be replacing the free Hypervisor. While Hyper-V Manager still works on Windows 10 and 11, it is unclear how long that will be the case.
VM configurations require licensing just like physical machines. The VM software installed on the host requires a license and the OS, and other applications installed on the VM also require a license. Since management and installation processes vary by vendor, employees will need training to match the chosen product.
Understanding how virtual machines operate in Hyper-V
VMs use a type of software called the hypervisor, and there are two types of hypervisors that form the foundation of the virtualization stack. As shown in Figure 2, Type 1 is bare metal, and it runs virtualization software such as Microsoft's Windows Core or VMWare's ESXi, which essentially becomes the OS, limited to virtualization. Figure 2 also shows Type 2 -- a hosted hypervisor -- which installs virtualization software on top of an OS. Examples of Type 2 include VMWare Workstation Pro, Hyper-V Manager and VMWare's GSX. Both types allow the creation of VMs that contain disk space, memory, CPU, network interface and other computer resources, within which an admin can install an OS and add applications.
Microsoft's Hyper-V Manager provides excellent insight as to how this works. Admins can enable Hyper-V in Windows 10 and 11 by finding Windows Features and selecting Turn Windows Features On and Off and then Virtual Machine Platform and Windows Hypervisor Platform (Figure 3). This requires a reboot. After the reboot, search for Hyper-V Manager and open the management interface.
Figure 4 shows the Hyper-V Manager dialog running on a laptop, listing several VMs -- clients and servers. In the upper right of the dialog, clicking Quick Create launches a Wizard to create a new VM. The wizard will ask about the amount of physical resources to allocate to the VM. This allocation will deplete the physical machine's resources available to the host OS. For example, if the host has 10 GB RAM and 4 GB is allocated to a VM, the host OS only has 6 GB RAM to use for other tasks.
However, Memory, CPU, and network resources are only depleted from the host when the VM is running. Thus, admins can create multiple VMs, with each using 4 GB of RAM.
Disk storage is another matter. When allocating disk for a VM, remember it depletes even when the VM is turned off since the VM file has to exist on the disk prior to starting. If an admin needs more VMs, they can just reduce the RAM on the VMs. Additional functionality at least for Hyper-V includes the following:
- Portability because admins can move VMs from one server to another depending on the VM OS used, since they are just a file. Follow the OS configuration requirements to duplicate instances.
- VM resources can be changed when the VM is offline, as shown in Figure 5.
- VMs can be managed in the VM window to start, stop, shut down, pause, access media, and more.
- Admins can make and save software checkpoints on the Host disk. When a checkpoint exists, there will be a prompt when the VM starts that asks if the admin wants to start from a checkpoint save -- known as a revert -- or continue on from the last shutdown (Figure 6).
- Admins can create a virtual network and manage it in Hyper-V, allowing networking of VMs on a virtual standalone network or interfacing with the physical network.
How does virtual desktop infrastructure affect virtual desktop function
VDI takes simple virtual machine technology to a different level. Advanced by VMWare, Citrix and others, this is a more complex and expensive technology that uses a desktop, laptop or server to host multiple VMs.
VDI can be a rack of shared server-storage managed by special software and deploy desktops to physical clients as an application would be. This provides powerful management capabilities for the IT staff to lock down and manage clients without having to visit or touch them. It could also be physical rack mounted desktops that display their image to the physical client in local or remote locations.
Though VDI is powerful, it is often considered difficult, confusing and expensive. VMs ultimately require physical resources that have to be allocated to the VM.
From the user perspective, a user can log in to their physical client -- a desktop or laptop -- open a browser or click on an application icon. Then, they can open a window that will function as a new desktop. They can perform their work on the desktop that is loaded with company-approved applications and access required data sources. In addition, the physical machine can boot up from a remote VM using the vendor's software.
Imagine the power of VDI for environments where users have temporary workspaces. The user could log in to any client, have their desktop environment displayed for work, then log off and have it all saved in the VM. They could travel to another office the next day, log in to one of their physical machines and load their desktop again to that machine and they're in business without having to carry a laptop or be limited to a certain device.
The IT staff loves it because they have total control of all desktop environments and don't have to visit physical machines. With more powerful client computers, IT could build a small network of a server and a couple of workstations on a laptop.
VDI provides robust security and a powerful and flexible remote workspace for users. Although implementing a VDI is complicated and expensive, in the right environment and with a skilled IT staff, the advantages often overcome the disadvantages.
Gary Olsen has worked in the IT industry since 1983 and holds a Master of Science in computer-aided manufacturing from Brigham Young University. He was on Microsoft's Windows 2000 beta support team for Active Directory from 1998 to 2000 and has written two books on Active Directory and numerous technical articles for magazines and websites.
