Integration of the host operating system with a guest virtual machine can be described as:
Integration features are not available until the Integration Components (or ICs) are installed on a guest VM. Basic integration is activated by installing the ICs on the guest. Enhanced integration is activated by enabling the Integration Features. Here’s an overview of what you’ll find with the 3 levels of host-VM integration.
When the ICs are not installed on a guest VM, the only built-in interaction between the host and the guest is through an emulated “native” console (VMWindow.exe). The benefit of this method is that the user can interact with the virtual machine from the beginning of the boot process before the guest operating system has been initialized, and it even allows the user to enter the setup for BIOS. The main disadvantage is the lack of certain features, such as the redirection of host devices to the guest machine. For instance, mouse movement will not be seamless across host and guest. The mouse will be stuck inside the guest window, or it will be outside the guest window. The user must use the host key combination, Ctrl+Alt+Left Arrow, to leave the guest window.
- Time synchronization between guest and host This is responsible for synchronizing the date and time on the guest operating system with the host. For example, if the time (System clock) is out of sync because the system is sleeping or hibernating, the time synchronization feature is used to force an adjustment after the machine wakes up. The time synchronization feature also periodically adjusts the guest VM time if it is out of sync due to clock drift. Additionally, the time settings of the guest are synchronized with the host during a boot operation. Note that the synchronization operation does not affect the time zone or Daylight Savings Time settings on the guest. The date and time are adjusted based on the GMT date and time derived from the host machine.
- Guest heartbeat monitoring The heartbeat provides a mechanism to detect an unresponsive (crashed, blue-screened, or hung) guest VM. Heartbeat requests are sent every 60 seconds by the host. If the guest is unresponsive, three retries are made for getting the response. If the correct response is not received within the allowed latency, the guest is declared dead. The heartbeat information flow consists of a heartbeat request sent from the host to the guest followed by a response sent from the guest to the host.
- Host-initiated shutdown This feature allows shutdown of the guest operating system with a request message generated by the host. COM APIs provide the messaging channel. The options available through the virtual machine window are Sleep, Restart, Hibernate, Shutdown, and Turn Off. The API also provides the option to log off the current user.
- Guest video resize (arbitrary guest resolution) This is a feature of Virtual PC (VPC) by which the guest resolution is changed in basic mode when the guest window is resized such that the guest desktop fits in the host side VM window.
- Mouse movement across host and guest The same “native” console emulation available when Integration Components are not installed is available in basic mode. But because the mouse integration component is activated in basic mode, a user can move his mouse pointer inside and outside the virtual machine window without using the release key.
- Audio This controls whether audio input and output for the virtual machine is redirected to audio devices in the host or is managed by an emulated audio device. To improve audio performance, clear the check box for a virtual machine running Windows XP, and select the check box for a virtual machine running Windows Vista or Windows 7. Note that for Windows Vista and later guest operating systems, a virtual audio device is used for redirection of sound from the guest to the host. For earlier versions of Windows, a SoundBlaster 16 audio adapter is emulated.
- Clipboard This lets you copy and paste data and files between the host operating system and the guest operating system. For example, you can copy a URL from the browser in a guest OS and paste it into a browser in the host OS.
- Printer This IC lets the user redirect printing from the guest machine to printers on the host machine. Note that if you want to share printers when Windows XP is the guest OS, you must install the printer drivers. (In enhanced mode, the drivers need to be present on the host and on the guest. However, basic mode does not require host side drivers to be present.)
- Smart Cards This IC supports smart cards connected to the host inside the guest OS. Smart-card redirection works similarly to printer redirection.
- Drives This shares the drives you select on the host with the virtual machine so that you can easily access host data from within a VM. This also makes it possible to access the host desktop and Documents folder from virtual applications when you select those resources to share. Note that host hard drives are listed in the guest operating system by using the computer name of the host operating system. For example, on a host computer named WindowsTest, the C drive will be listed in the guest OS as “C on WindowsTest”.