Abstract: An incremental garbage collector which permits a memory allocator's decommit mechanism to operate while the garbage collector is detecting memory that a program being executed is certainly not using. The garbage collector includes a decommit barrier which prevents the garbage collector from referencing memory that the allocator has decommitted from the address space of the process on which the program is executing. In mark-sweep incremental garbage collectors, the decommit barrier may be implemented in two ways: by means of a table which the allocator marks whenever it determines that a portion of memory is subject to being decommitted from the process's address space and which the garbage collector examines before scanning the portion and by means of a table which the garbage collector marks when it finds that a portion of memory must be scanned and which the allocator examines before decommitting the portion.