that wants to enter a server system broadcasts an inquiry message to other servers to inform them of its entry, si requests a current value of the register. Once other server receive this inquiry they send reply messages to si. After si receives enough replies from other servers, it collects the replies and saves them into a reply set. Si waits until it gets enough replies (n-f-j) from other servers then it picks the most frequently received value. Si also: Updates its local copy of the register Becomes active Replies to the processes in the reply set If it becomes active it sends reply messages to the other servers. Otherwise, it stores the inquiries, replying when it becomes active. When it gets replies from other servers it adds the new reply to the reply set and discards the old value. If the value of the responding server is bigger than si's value, si retains the new value. Read The read algorithm is a basic version of join. The difference is the broadcast mechanism used by the read operation. A client (cw) broadcasts a message to the system and once a server receives the inquiry, it sends a reply message to the client. Once the client receives enough replies (n-f-j) it stops sending an inquiry. Write Client (cw) sends an inquiry into the system in different rounds and waits until it receives two acknowledgment. (sn =sequence number) The reason for receiving two acknowledgments is to avoid danger in a system. When a process sends an acknowledgement (ack), it may die after one millisecond. Therefore, no confirmation is received by the client. The validity of the safe register (If a read is not concurrent with any write, return the last value written) was proved based on the quorum system. Given two quorum systems (Qw, Qr) Qw indicates the servers that know about the latest value, and Qr indicates values of read responses. The size of each quorum is equal to n-f-j. Proving the safe register's validity requires proving were B is the number of Byzantine failures. Proof : Red region indicates (Qw∩Qr)\B and the blue region indicates Qr∩B. From the assumption, the size of each quorum is n-f-j, so the red region has n-3f-2j active servers. Therefore, is strictly greater than f. Notes See also Regular semantics Atomic semantics Concurrency control