Integrity S2: a fault-tolerant Unix platform

A description is given of Integrity S2, a fault-tolerant, Unix-based computing system designed and implemented to provide a highly available, fault-tolerant computing platform for Unix-based applications. Unlike some other fault tolerant computing systems, no additional coding at the user-level is required to take advantage of the fault-tolerant capabilities inherent in the platform. The hardware is an RISC-based triple-modular-redundant processing core, with duplexed global memory and I/O subsystems. The goals for this machine, the system architecture, its implementation and resulting performance, and the hardware and software techniques incorporated to achieve fault tolerance are discussed. Fault tolerance has been accomplished without compromising the programmatic interface, operating system or system performance.<>