Virtualization allows computing resources like storage, I/O, and interconnects to be shared across virtual machines through emulation, paravirtualization, or operating at the OS or API level. Popular virtualization platforms include Qemu, Xen, OpenVZ, and WINE which can emulate or virtualize at different levels. Virtual machines are managed through tools that allow starting, stopping, migrating, and monitoring large numbers of instances, though standardizing management via CIM and WBEM remains problematic. Virtualization is also related to grid computing by providing a runtime environment and addressing security issues.