A method of implementing virtualization involves an improved approach to resource management. A virtualizing subsystem is capable of creating separate environments that logically isolate applications from each other. Some of the separate environments share physical resources including physical memory. When a separate environment is configured, properties for the separate environment are defined. Configuring a separate environment may include specifying a physical memory usage cap for the separate environment. A global resource capping background service enforces physical memory caps on any separate environments that have specified physical memory caps.