1. A computer program product for protecting data 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 initial origin of a translation table of said hierarchy of translation tables, said hierarchy of translation tables comprising a segment table; based on the obtained initial origin, obtaining a segment table entry from said segment table, said segment table entry configured to contain a format control field; in response to an enhanced DAT facility being enabled, determining whether said format control field in said segment table entry is enabled; and in response to said format control field being enabled, performing: determining whether said access validity field in said segment table entry is enabled, said segment table entry comprising said access validity field, a segment access control field, a segment fetch protection field and a segment-frame absolute address of a large block of data in main storage; and in response to said access validity field being enabled, performing: permitting stores to said desired block of memory, wherein the stores are associated with the virtual address, said stores permitted only in response to said segment access control field matching a program access key provided by any one of a Program Status Word or an operand of a program instruction being executed; and permitting fetches from said desired block of data, wherein the fetches are associated with the virtual address, only in response to either a) the segment fetch protection field being disabled, or b) in response to both the segment fetch protection field being enabled and the program access key associated with said virtual address being equal to said segment access control field.