STAR computer has five redundant modular function units, fixed store, arithmetic, memory, input, and output. Each unit is connected to a diagnostic control unit, each is coded for error detection and error correction. Separation into function units permits assembly of many different systems from the set of units

Avizienis, A. A.

English

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September 1970	 Brief 70-10452 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Self Testing and Repairing Computer: A Concept 
Main Power 
Control Inputs From CDU	 Status Outputs to CDU

Conceptual Schematic 
The immediate use for the prototype model of the 
self testing and repairing (STAR) computer is to in-
vestigate and revaluate the concept of a computer 
that checks both the data and the instructions. Such 
a computer could be applied to process control com-
puters where stopping the computer is not possible 
when a fault is noted, and would be valuable in air-
line reservation computer systems having many ter-
minals, or in any real-time systems. The prototype of
this system now under construction is the only existing 
practical hardware in the computer field. 
The STAR computer is made up of redundant mod-
ular function units. These function units, illustrated 
in the figure, are of several types and are connected to 
a diagnostic control unit. The most obviously needed 
types of function units required for some applications 
are (1) fixed store; (2) arithmetic; (3) memory; (4) in-
put; and (5) output. Other units may be found neces-
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned .rights.
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https://ntrs.nasa.gov/search.jsp?R=19700000436 2020-03-17T00:49:37+00:00Z
sary, for instance, system clock, or scientific data 
reducer units. 
Fixed store function units will contain sequencing 
programs for guidance computations, and all emer-
gency, diagnostic, and other internal procedures. 
Scientific data reduction programs may also be con-
tained here. The program data (instructions) will be 
coded for detection of errors and failure. The redun-
dancy will be in the form of reserve units; time redun-
dancy(repeated readout) may also be used to determine 
if an error in a word is transient or due to component 
failure. 
Arithmetic function units must have a provision to 
retain the error-detecting code in the results of arith-
metical operations. Furthermore, an independent in-
dication of which arithmetic operation has been per-
formed is desirable with the result; in this manner, 
improper interpretation of the instruction by the 
arithmetic unit can be detected. - 
Memory function units are used for storage of 
intermediate results and other non-fixed information. 
Two units are likely to be used at once to avoid loss 
ofinformation; an error correcting code is used also. 
An independent indication (to the Diagnostic Control 
Unit) of the address from which (or into which) in-
formation was delivered avoids errors due to incor-
rect address decoding. 
Input function units are composed of various sen-
sors and transducers and the radio receiver. Input 
data appears in digital form and is coded in an error 
detecting code. Such code may appear on shaft po-
sition digitizers. Validity check is available at each 
input. Spare input devices are available for self re-
pair.
The radio receiver is expected to deliver coded in-
formation which can be checked for validity; a spare 
receiver is desirable. 
Output function units are the various actuators 
and the radio transmitter. An independent feedback 
of the output information as delivered by the output 
units provides a check of their performance. Voting 
type redundancy of actuators is used. A spare radio 
transmitter is desirable. 
The separation into function units allows most 
flexibility in assembling a complete STAR system; 
onlS' the format of information must be retained. Thus 
many different systems may be put together from the 
set of units. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B70-10452 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: Algirdas A. Avizienis of 
-	 Caltech/JPL 
under contract to 
NASA Pasadena Office 
(NPO- 10567) 
Brief 70-10452	 Category 09


Self testing and repairing computer - A concept

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