VirtualBox is a powerful virtualization software that allows users to run multiple virtual machines on a single physical host computer. It works by creating virtualized hardware environments in which operating systems can be installed and used as if they were running on real hardware. In this article, we will explore how VirtualBox creates and manages these virtual machines to provide a seamless virtualization experience.
What is VirtualBox?
VirtualBox is a cross-platform virtualization application developed by Oracle. It installs on an existing host operating system as an application and allows you to install additional guest operating systems within it. These virtual machines can then run applications, games, system tools, and more as if they were installed on a stand-alone physical computer.
Some key features of VirtualBox include:
- Open source virtualization software
- Available for Windows, Linux, Mac OS, and Solaris hosts
- Supports a wide range of guest operating systems including Windows, Linux, Solaris, and others
- Easy to install and configure virtual machines
- Virtual machine snapshots allow you to save a machine state and revert back to it later
- Virtual networking and DHCP for configuring host-only networks
- Shared folders allow seamless data transfers between host and guests
- Strong visualization capabilities using Remote Desktop Protocol and VRDP
With these features, VirtualBox provides a powerful tool to run, test, and manage multiple operating systems and environments all on one physical computer.
How does virtualization work?
To understand how VirtualBox works, it helps to first look at how hardware virtualization in general functions. The key concept is virtualization allows you to abstract the hardware layer away from the software layer. Software running inside a virtual machine believes it is running on real physical hardware, when in reality the hardware resources are being shared and managed by the virtualization software (VirtualBox).
Some of the key virtualization techniques used by VirtualBox include:
- Binary Translation: VirtualBox can dynamically translate code from guest virtual machines into code that is optimized and executable for the host hardware. This provides portability across different CPU architectures.
- Paravirtualization: The guest OS is modified to replace non-virtualizable instructions with hypercalls that communicate directly with the virtualization layer for improved performance.
- Hardware-assisted virtualization: Features like Intel VT-x and AMD-V allow VirtualBox to better utilize the native hardware capabilities for virtualization.
Using these techniques, VirtualBox can provide critical components like virtualized CPUs, memory, storage, graphics, input devices, and networking. The guest operating systems interact with what looks like real hardware, without knowing it is being shared across virtual machines.
Key Components of VirtualBox
When installed on a host computer, VirtualBox consists of several key software components that work together to create and run virtual machines.
1. VirtualBox Manager
The VirtualBox Manager provides the main user interface and tools to configure, control and manage your virtual machines. It allows you to:
- Create new virtual machines
- Configure hardware settings for VMs
- Install guest operating systems
- Start, stop and pause virtual machines
- Adjust VM resources like processor cores, memory and graphics
- Manage storage for virtual drives
- Establish virtual networking
The Manager provides a central place to manage every aspect of your virtual environments.
2. VirtualBox Core (VMM)
The VirtualBox Core or virtual machine monitor (VMM) is the underlying hosted hypervisor that creates and runs your virtual machines. It handles processor virtualization, memory management, virtual hardware, guest OS loading and execution, and more. The VMM isolates and sandboxs each VM from the host system and other VMs.
3. VirtualBox Guest Additions
The VirtualBox Guest Additions consist of device drivers and system applications that are installed inside the guest OS to improve performance and add functionality. This includes features like:
- Mouse pointer integration
- Shared folders
- Better video and graphics
- Time synchronization
- Shared clipboard
The Guest Additions are typically installed after you set up a new virtual machine and install the guest OS.
4. Remote Desktop
VirtualBox uses Remote Desktop Protocol (RDP) to access and control guest OS graphical interfaces. Remote Desktop allows you to view and interact with the screen of a virtual machine as if using a physical monitor, keyboard, and mouse attached to that VM.
How VirtualBox Creates Virtual Machines
When you create a new virtual machine in VirtualBox, it goes through the following key steps:
- You configure a new VM and allocate resources like RAM, virtual storage, CPUs, etc.
- VirtualBox creates VM configuration files defining the hardware, storage, network, and other settings.
- A virtual hard disk file (.vdi) is created which will act as the main storage drive for the VM.
- You install a guest operating system (OS) into the new VM.
- The VirtualBox Extension Pack adds additional hardware support if needed by the guest OS.
- You install the VirtualBox Guest Additions into the new VM to optimize performance.
- The VM can now be powered on and booted up like a real computer.
From the guest OS point of view, it believes it is running on a real dedicated PC. But under the hood VirtualBox is translating requests from the VM to the physical resources of your host computer.
Key Processes When Running Virtual Machines
Once up and running, VirtualBox uses several concurrent processes and techniques to manage your virtual machines:
CPU Scheduling and Optimization
VirtualBox schedules virtual CPUs (vCPUs) on your system using sophisticated partitioning algorithms. This allows multiple guest VMs to share the physical CPUs on your host while optimizing performance and utilization. CPU and IO priorities can be adjusted dynamically based on VM workloads.
Memory Management
Physical host RAM is allocated to each VM per its settings. VirtualBox uses advanced memory optimization techniques so VMs can share memory efficiently. Unused memory can be re-allocated across VMs as workloads change. Memory swapping and ballooning adjusts memory on the fly.
Storage Emulation
Virtual hard disks emulate real hardware but data is stored in vdi container files. When a VM writes data, VirtualBox translates and stores it in the virtual disk file behind the scenes. Disk images can be dynamically sized or optimized as well.
Virtual Networking
Software like DHCP and virtual Network Address Translation (NAT) is used to establish TCP/IP networking between VMs and the host system. Bridged, host-only, internal, and NAT networks can be configured providing full network connectivity.
Graphics and Audio
The VirtualBox graphics card emulation uses your actual graphics hardware to render graphics and frames for each VM. Remote Desktop Protocol (RDP) can be used for full remote access. Audio is passed from VMs to the host sound device using pulse audio.
By coordinating these and other processes, VirtualBox is able to route I/O, resources and communications from the guest VMs to the host hardware transparently and efficiently.
Benefits of Hardware Virtualization
There are many benefits to using hardware virtualization with solutions like VirtualBox for tasks like development, testing, sandboxing, and running multiple operating systems on one computer:
- Isolation – VMs are completely isolated from the host OS and hardware.
- Security – Enhanced security by compartmentalizing apps and processes into separate VMs.
- Compatibility – Support a wide range of OSes on one system including older legacy environments.
- Development – Test software and websites in different environments quickly.
- Testing – Test apps across multiple OS versions and configurations.
- Sandboxing – Safely run untrusted software in isolated virtual environments.
- Migration – Move and run VMs across different host systems.
By providing these advantages, VirtualBox has become a widely used tool for programmers, system administrators, product testers, and savvy home users alike.
Conclusion
In summary, VirtualBox is an extremely versatile virtualization platform. Some of the key points on how it works include:
- Creates virtualized hardware environments called virtual machines (VMs) that guest OSes run on.
- Leverages hardware-assisted virtualization features on Intel VT-x and AMD-V CPUs.
- The VirtualBox Manager provides full configuration control over VMs.
- The VirtualBox hypervisor isolates and runs VMs using dynamic resource optimization and allocation.
- Guest Additions improve integration, performance and usability.
- Remote Desktop Protocol (RDP) allows viewing guest OS interfaces.
- CPU, memory, storage, networking are all virtualized at the hardware level and shared between VMs.
By seamlessly virtualizing hardware and resources, VirtualBox provides a powerful and portable virtualization solution across a wide range of host and guest operating systems.