A technique that prohibits one program in memory from accidentally clobbering another active program in memory. Using various methods, a protective boundary is created around the program, and instructions within the program are prohibited from referencing data outside of that boundary. When a program erroneously points to data or instructions beyond its boundary, earlier personal computer operating systems, such as DOS, Windows 3.x and Windows 95/98, simply froze (crashed, bombed). Operating systems such as Unix, Linux and subsequent versions of Windows are more robust and generally allow the errant program to be closed without affecting the remaining active programs. See abend and memory.