1. A method of restricting guest operations in a data processing system to system resources assigned to a guest, the resources in the system including one or more real CPUs, a system main storage (MS), an optional system extended storage (ES), and a plurality of I/O channels using I/O processors for connecting to the system a plurality of I/O device control units with their I/O devices, a host hypervisor (host) which includes software, the host supervising plural software control programs (guests) capable of concurrently and independently operating in the system and the guests may be the same or different types of control programs, subchannels (SCHs) for representing I/O devices to the host and to the guests, each guest being restricted to using an assigned subset (partition) of system resources, the method for restricting guest operations comprising: providing a plurality of partition sets in system storage for defining partitions of system resources, each partition set defining a particular subset of system resources available to a guest assigned to use the partition, each partition set comprised of a plurality of entries for specifying the system resources assigned to the partition and the items being enterable by a human operator, the items assignable to each partition set including indicators for: a unique partition identifier (AZN), a MS zone of contiguous main sotrage which can be located anywhere in MS and bounded by upper and lower limit MS addresses, none or mone or plural SCHs, and an optional ES zone located anywhere in ES and bounded by upper and lower limit ES addresses, having a control block in system storage for each SCH, each SCH containing an identifier for an I/O interrupt queue assigned to the SCH, each SCH being capable of being assigned to none, one or plural partition sets as indicated by none, one or more AZNs being set into the control block of the SCH, also having a plurality of state description control blocks (SDs) in system storage for representing logical CPUs in the system, each SD containing fields with parameters for defining a logical CPU, binding a logical CPU to a particular partition by entering the AZN of a respective partition set into the SD representing the logical CPU, assigning a logicl CPU to a particular guest by entering parameters of the guest into the SD of the logical CPU, dispatching a logical CPU for a guest on a selected real CPU in the data processing system by the host executing a start interpretive execution (SIE) instruction on the real CPU to start execution of the logical CPU for the guest in the partition assigned by the AZN in the SD of the logical CPU, assigning an I/O device to a guest by setting the AZN assigned to the guest's partition set into an SCH of the I/O device and setting an identifier of the SCH into the guest's partition set and into the SD of each logical CPU which is to use the SCH, setting a pass-through indicator in a SCH of an I/O device assigned to a guest to enable the direct routing of I/O instructions from, and of pending I/O interruptions to the logical CPU of the guest in order to allow each guest to directly control guest assigned I/O devices without host assistance during normal execution of I/O operations by a guest's logical CPU, allowing a guest to directly insruct, and to directly handle I/O interruptions for, an I/O devie assigned to the guest by determining that the SCH of the I/O device is set with the same AZN as is set into the SD of the logical CPU dispatched for the guest to allow the guest to control its assigned I/O devices without host intervention, and to restrict each guest to using only the SCHs having the same AZN identified in both the SCH and the partition set assigned to the guest.