Tandem Computers Incorporated

Brian Vetter

Douglas E Jewett

Tom Bereiter

Richard W Cutts, Jr

Nikhil A Mehta

Kenneth C Debacker

Randall G Banton

Donald C Westbrook, Deceased

John Pozdro

Kyran W Fey, Jr

A fault-tolerant computer system employs a pseudo-filesystem to dynamically manage the hardware components. A directory which appears as a standard, hierarchical directory in this filesystem contains a file for each component; each file maps to either a hardware component or a software module. The pseudo-filesystem hierarchy is determined during system initialization and is automatically updated whenever the software or hardware configuration changes. The pseudo-filesystem, called /config filesystem herein, is implemented as a Unix filesystem in the Unix filesystem switch. This pseudo-filesystem method may be implemented in a fault-tolerant, redundant computer system configuration having multiple identical CPUs executing the same instruction stream, with multiple, identical memory modules in the address space of the CPUs storing duplicates of the same data. The system detects faults in the CPUs and memory modules, and places a faulty unit offline while continuing to operate using the good units. The multiple CPUs are loosely synchronized, as by detecting events such as memory references and stalling any CPU ahead of others until all execute the function simultaneously; interrupts can be synchronized by ensuring that all CPUs implement the interrupt at the same point in their instruction stream. Memory references are voted at the three separate ports of each of the memory modules.

Fault-tolerant computer system with /CONFIG filesystem

A computer system in a fault-tolerant configuration employs multiple identical CPUs executing the same instruction stream, with multiple, identical memory modules in the address space of the CPUs storing duplicates of the same data. The system detects faults in the CPUs and memory modules, and places a faulty unit offline while continuing to operate using the good units. The faulty unit can be replaced and reintegrated into the system without shutdown. The multiple CPUs are loosely synchronized, as by detecting events such as memory references and stalling any CPU ahead of others until all execute the function simultaneously; interrupts can be synchronized by ensuring that all CPUs implement the interrupt at the same point in their instruction stream. Memory references via the separate CPU-to-memory busses are voted at the three separate ports of each of the memory modules. I/O functions are implemented using two identical I/O busses, each of which is separately coupled to only one of the memory modules. A number of I/O processors are coupled to both I/O busses. I/O devices are accessed through a pair of identical (redundant) I/O processors, but only one is designated to actively control a given device; in case of failure of one I/O processor, however, an I/O device can be accessed by the other one without system shutdown.

Fault-tolerant computer system with online recovery and reintegration of

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Brian Vetter