The article discusses an approach to the quality management system of digital systems, which unites all stages of the life cycle. Some aspects of quality assurance in digital systems development were considering this approach, and the main factors of unsatisfactory quality were noted. The core of the digital system is system and application software; therefore, special attention is paying to the consideration of software errors (their categories and consequences) and the principles of building reliable software used in the development of software for upper-level digital systems of NPP APCS.