United States Patent im [in Patent Number: 5,005,174
Bruckert et al.  Date of Patent: Apr. 2,1991
 DUAL ZONE, FAULT TOLERANT COMPUTER SYSTEM WITH ERROR CHECKING IN I/O WRITES
William F. Bruckert, Northboro, Mass.; Thomas D. Bissett, Derry, N.H.
Digital Equipment Corporation,
4,541,094 9/1985 Stiffler et al. .
4,610,013 9/1986 Long .
4,654,857 3/1987 Samson .
4,751,702 6/1988 Beier .
Primary Examiner— Jerry Smith
Assistant Examiner—Robert W. Reausoliel
Attorney, Agent, or Firm—Finnegan, Henderson,
Farabow, Garrett, and Dunner
 Appl. No.: 489,751
 Filed: Feb. 26,1990
Related U.S. Application Data
 Continuation of Ser. No. 93,572, Sep. 4, 1987, abandoned.
 Int. CI.' G06F 11/16
 U.S. a 371/68.3; 364/268.3;
r58] Field of Search 371/68.3, 68.1, 9.1,
371/8.1, 7; 364/187, 200 MS File, 900 MS File
 References Cited
U.S. PATENT DOCUMENTS
A fault tolerant computer system having a first processing system which includes a first data processor for executing a series of data processing instructions. A first data output terminal outputs data from the first processing system. A second processing system, substantially identical to the first processing system, operates independently from the first processing system. The second processing system includes a second data processor for executing the series of data processing instructions in the same sequence as the first data processor. It also includes a second data output terminal for outputting data from the second processing system. A synchronizing device is coupled to the first and second data processors for maintaining the execution of the series of data processing instructions by the first and second processing systems in synchronism. Fault detection devices are coupled to the first and second data output terminals for comparing the data output from the first processing system with the data output from the second processing system. The fault detection devices identify the presence of an error when the data output from the first processing system at the first output terminal is different from the data output from the second processing system at the second output terminal.
18 Claims, 53 Drawing Sheets