Wayne A Robbins

US Patent:

43216676, Mar 23, 1982

Filed:

Oct 31, 1979

Appl. No.:

6/089799

Inventors:

Wayne E. Robbins - Longmont CO
Paul R. Spivey - Winchester KY
Terence Travis - Boulder CO

Assignee:

International Business Machines Corp. - Armonk NY

International Classification:

G06F 1306

US Classification:

364200

Abstract:

Expandable memory system having add-on modules beginning at fixed address boundaries, e. g. , 2K (K=1024), and having verification and authorization features. A non-volatile memory stores a bit corresponding to each 2K memory boundary. When an add-on program is authorized at a particular boundary address, the corresponding bit is set. The base program checks each bit and, if it is set, reads the first location of the corresponding add-on program. If the data read from the new module matches some reference, e. g. , the boundary address itself, then program control branches to the add-on program. Additional verification features include cyclic redundancy checks of the added code. Alternative operation includes branching to a verified add-on program that tests its own authorization bit which, if reset, causes a branch to the next verified add-on program, and so on.