Guest/host extended addressing method and means with contiguous access list entries

An addressing method using large addresses in a guest/host environment within a computer system. The guests are operating-systems, and the host is a hypervisor program. Each guest has a guest real address space (guest RAS) mapped onto a host large real address space (host LRAS) using means disclosed herein. To do this, each guest RAS is first assigned to a contiguous part of a host large virtual address space (LVAS) by assigning each guest RAS to one or more contiguous units of virtual addressing in the host LVAS, each unit having a 2 gigabyte (GB) size. The host LVAS is represented by a sequence of entries (ALEs) in a host access list (AL), in which each ALE represents a 2 GB unit of virtual addressing in the host LVAS. An ALE is selected in the AL by using a high-order part of a host large virtual address (host LVA) representing a guest RA or LRA. A host LVA is generated from a guest RA for obtaining the guest address in host main storage. The host LVA is translated in a number of different ways to a host LRA, depending on the type of guest providing the corresponding guest RA or LRA. The guest types include V=V, V=FC, V=FD and V=R guests, which is indicated in a guest control block (GCB).