According to Armstrong’s thoughts, the architecture for building fault-tolerant systems could be described as follow:

• Completely modular. Each module must be independent of the other modules and should run in a different process. Of course processes must run in parallel.
• Provide fault-isolation. Failure in one process should not adversely affect other processes (unless it has been intentionally designed).
• Communication based on messages: Each process should have a unique identifier, and can communicate each other only using messages. There should be nothing shared among them. Also a communication protocol should exists and the messages passing should be asynchronous.

Armstrong also mentions the fail-stop processor. Such processor should halt on failure (if a failure occurs it is pointless to continue), communicate the cause of the failure to other processors and have both stable and volatile storage.