Requirements for functions, performance, and interface and environmental conditions for vital computers used in rail safety-related systems are established in this recommended practice. Vital computer functions are developed based on the technology of computer systems, communication, and functional safety as well as security considerations. A vital computer is composed with basic functional modules such as main process, input, output and communication. This recommended practice can be applied to vital computers for onboard and wayside equipment in rail applications. Application systems which are developed based on vital computers are not covered, but safety-related conditions for application systems are proposed. The internal structure and the technical realization of the vital computer are not constrained in this recommended practice.