Protection Scheme for Non-Key Storage Systems
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
In various systems having small work stations in which storage keys are not implemented, the possibility exists of accessing and destroying the supervisor software by the user software. A scheme is provided which generates an exception to the user software accessing the supervisor software by flagging the supervisor for error correction. The supervisor program resides contiguously at the high end 1 (Fig. 1) of the virtual space, and user programs 2 reside below the supervisor program 3. The supervisor program size may vary from 64 Kb to 16 Meg minus 128 Kb in 64 Kb increments, as seen in the virtual memory map (Fig. 1). The supervisor boundary register 4 (Fig. 2) is initialized to X'FF' when the system is powered on, thus bypassing the protection mechanism.