: Due to advances in mission complexity and increased requirements for autonomous control of small satellites, high-level computing performance of on-board computers, as well as the necessary software implementation to maintain essential functionality, is more frequently required for small satellites. To satisfy these requirements, we developed a high-performance and compact on-board computer for micro and nano-satellites using commercial off-the-shelf (COTS) components including a structure to increase the reliability by sharing software to enhance reusability. The capability of small satellites can be dramatically improved by having common standards for high computing performance and a lowcost platform for the on-board computers. Additionally, the mission potential of small satellites can then be expanded. When the same platform is utilized recursively, the reliability of the platform will increase through repeated verification. In this paper, we describe the concept of a high-performance, low-cost on-board computer system using COTS devices, the sharing of software resources, and a practical on-orbit evaluation of the system.