**Abstract**

Billions of transistors on a chip have led to integration of many cores leading to many challenges such as increased power dissipation, thermal dissipation, occurrence of faults in the circuits, and reliability issues. Existing approaches explore the usage of redundancy-based solutions for fault tolerance at core level, thread level, microarchitectural level, and software level. Core-level techniques improve the lifetime reliability of multi-core systems with asymmetric cores (large and small cores), which have gained momentum and focus among a large number of researchers. Based on the above implications, multi-core system using one instruction cores (MCS-OIC) factoring its features are proposed in this chapter. The MCS-OIC is an asymmetric multicore architecture with MIPS core as the conventional core and OICs as the warm standby-redundant core. OIC executes only one instruction named 'subleq \_ subtract if less than or equal to zero'. When there is one of the functional units (i.e., ALU) of any conventional core fails, the opcode of the instruction is sent to the OIC. The OIC decodes the instruction opcode and emulates the faulty instruction by repeated execution of the 'subleq' instruction, thus providing fault tolerance. To evaluate the idea, the OIC is synthesized using ASIC and FPGA. Performance implications due to OICs at instruction and application level are evaluated. Yield analysis is estimated for various configurations of multi-core system using OICs.

**Keywords:** fault tolerance, reliability, one instruction core, multi-core, yield
