a data processing system operated with multiple levels of virtual machine guests under a host control program . the second level of guests are invoked , operated , and terminated without host intervention , as has been required in prior systems , to significantly increase the operating efficiency of the system . address translation is done by providing machine capability to translate second level guest addresses to real memory addresses taking advantage of the first level guest being located at a simple offset within real memory . special facilities for second level guests periodically test for timing interruptions for second level guests and update the second level guest timing facilities .