However, real computers are faulty; they fail and recover from failure at unpredictable, possibly inopportune, times.
[1] A number of protocols have been proposed for performing atomic broadcast, under various assumptions about the network, failure models, availability of hardware support for multicast, and so forth.
This was demonstrated more formally and in greater detail by Xavier Défago, et al.[2] A fundamental result in distributed computing is that achieving consensus in asynchronous systems in which even one crash failure can occur is impossible in the most general case.
This was shown in 1985 by Michael J. Fischer, Nancy Lynch, and Mike Paterson, and is sometimes called the FLP result.
[8][9] Ken Birman has proposed the virtual synchrony execution model for distributed systems, the idea of which is that all processes observe the same events in the same order.