1. A computer program product for translation of a virtual address into a translated address of a desired block of main storage in a computer system of a machine architecture, the computer program product comprising: a storage medium readable by said computer system, said computer readable medium storing instructions for performing: obtaining the virtual address to be translated; obtaining an origin address of a translation table of a hierarchy of translation tables; using an index portion of said virtual address to reference an entry in said translation table; determining a value of a format control field in said translation table entry, said value being determinative of field function for one or more other fields in said translation table entry, a first value indicating that said translation table entry contains a large block address of a large block of main storage and an access restricting field, and a second value indicating that said translation table entry contains an origin address of another table of said hierarchy of translation tables; and responsive to said format control field having said first value, performing: obtaining from an address field in said translation table entry said large block address of said large block of main storage; additively combining said large block address with an offset portion of said virtual address to form said translated address of a desired block of main storage within said large block of main storage, said desired block of main storage consisting of one or more bytes; and accessing said desired block of main storage addressed by said translated address.