Browse Prior Art Database

EPROM Redundancy

IP.com Disclosure Number: IPCOM000034157D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Jacobson, DW: AUTHOR [+5]

Abstract

A redundancy scheme may be used to lower the failure rate of the EPROMs to lower than that of ROS, and thus allows the use of EPROMs in a final shipped product. The redundancy scheme includes using twice as much EPROM space as would be used in an ROS module. The extra storage is used to contain a second copy of the ROS code. When an error is found in the first copy of ROS code, the code and hardware switch to the second copy of ROS code, and therefore eliminate the need for a repair action in the field. Without redundancy, the failure rate of the EPROMs is 10.6 times as great as that of ROS. This is over the life of the product which is assumed to be 40K Power-on-Hours (POHs). When redundancy is used, however, the ROS modules now have a failure rate which is 12.5 times greater than that of the EPROMs.

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EPROM Redundancy

A redundancy scheme may be used to lower the failure rate of the EPROMs to lower than that of ROS, and thus allows the use of EPROMs in a final shipped product. The redundancy scheme includes using twice as much EPROM space as would be used in an ROS module.

The extra storage is used to contain a second copy of the ROS code.

When an error is found in the first copy of ROS code, the code and hardware switch to the second copy of ROS code, and therefore eliminate the need for a repair action in the field. Without redundancy, the failure rate of the EPROMs is 10.6 times as great as that of ROS. This is over the life of the product which is assumed to be 40K Power-on-Hours (POHs). When redundancy is used, however, the ROS modules now have a failure rate which is 12.5 times greater than that of the EPROMs. The number of projected failures of the EPROMs with redundancy is less than .8% of the total projected failures of the EPROMs without redundancy. Fig. 1 gives the cumulative percentage of modules failing by selected points in time for the ROS module and the EPROM with and without redundancy. For example, even though there is a 2.259% chance of an EPROM having a failure through 25K POH, there is only a (.5)x(2.259%)=1.13% chance of a failure in any particular half of the module. This is based on the assumption of single random bit failures which failure mode analysis shows to be the predominant cause of failure. Thus, there is a probability of (.0113)x(.0113)=.00013...