a virtual machine system which forms a hot standby configuration in a single computer system and effectively controls plural operating systems and application programs , and a method of allocating resources in the virtual machine system . plural operating systems are initiated with a small amount of main storage allocated to the individual operating systems , whereby the fixed amount of main storage allocated is reduced . when an application program is executed , a request to extend a resource is issued to a virtual machine monitor to obtain the resource , whereby an operating system newly allocates the resource to execute the application program . where a hot standby system is built using the virtual machine system , resources are reused by reallocating resources of the active operating system to a standby operating system .