Switching control in a fault tolerant system

A system comprising:

• a first server;
• a second server;
• a link over which the first server provides an indication to the second server of the activity state of the first server;
• and
• an expansion box having an expansion bus, the first and second servers being coupled to respective first and second slots on the expansion bus for communication with the expansion bus, wherein communication between the first server and the expansion bus is disabled by disconnecting the first server from the first slot and communication between the second server and the expansion bus is enabled by connecting the second server to the second slot if the indication indicates the first server is inactive.

A system comprising:

• a network;
• a first server connected to the network;
• a second server connected to the network;
• a serial link connected between the first and second servers, wherein the first server provides a heartbeat message to the second server over the serial link;
• and
• an expansion box having an expansion bus, a first expansion card connected to the expansion bus and the first server, and a second expansion card connected to the expansion bus and the second server, wherein output pins of the second expansion card are tri-stated if the heartbeat message is provided by the first server, and wherein output pins of the first expansion card are tri-stated and the output pins of the second expansion card are enabled if the heartbeat message has not been detected for a predetermined period of time.

A system comprising:

• a first system;
• a second system;
• a link over which the first system provides an indication to the second system of the activity state of the first system;
• and
• an expansion box including a bus having a first slot coupled to the first system and a second slot coupled to the second system, wherein communication between the first system and the bus is disabled by disconnecting the first system from the first slot if the indication indicates the first system is inactive, and communication between the second system and the bus is enabled by connecting the second system to the second slot if the indication indicates that the first system is inactive.