Redundancy
Every club asks this in the first call, and most software answers it with the word "redundancy" and no detail. Here is exactly what happens, in the order it happens, and what it needs from your rack.
The shape of it
What it actually is
A spare PC with the software installed is not redundancy. Somebody has to notice the wall has gone, find the machine, open the project, work out where the rotation had got to and start it, and by then the half is over and the sponsor has lost its seconds.
A USM backup PC runs the whole match alongside the main one. It holds the same project, it follows the same cues, and it knows which slot is on the wall right now, because it has been following all along rather than waiting to be woken. What it does not do is drive the wall, until the moment it has to.
The two machines talk on the venue network once a second. That is the whole failure detector: not a cloud service, not a person, not a monitoring dashboard that emails somebody. If the main stops answering, the backup already has everything it needs to take over, and it does.
The switch, second by second
An illustration, not a recording of one night: the times are the intervals the software actually works to, laid on a clock so the gap is visible.
Power, a kernel fault, a pulled cable. From the wall’s point of view the picture is still there: the LED processor is holding the last frame it was sent.
The backup was expecting a beat and did not get one. One missed beat is not a failure; a machine can be busy for a second.
Five seconds of silence is the threshold in the code. The backup promotes itself and drives the wall. It has been mirroring the master’s cues all match, so it knows the playlist and where the match had got to rather than starting cold.
Handing the wall back is a decision somebody makes, never automatic. Two machines both believing they are in charge is the one failure worse than the first, so USM makes an operator say which is which, and warns loudly on both screens if it ever sees two.
The parts that catch people out
What it takes
Being straight about it
There is a gap, and it is about five seconds long. If a sponsor rotation was due to change inside it, it changed late. We would rather write that down than describe a switch as instant.
We could make the gap shorter by treating a single missed heartbeat as a failure, and we do not, because a machine that is briefly busy would then hand the wall away in the middle of a match for no reason. Five seconds of a held frame is the cheaper mistake.
And the switch back is deliberately yours. Software that fails back on its own would produce a second transition at a moment nobody chose, usually while somebody is still working out what happened to the first machine.
Tell us how your two machines would be cabled and powered, and we will tell you honestly where the weak point is, including when it is not the software.