Semaphores, Mutices, fd_sets

[Greg Munt]

I've seen the words 'Semaphore' and 'Mutex' thrown about in RGMA lately. 
But I have no idea what they are. Would anyone be able to help me out?

Also, an fd_set holds FD_SETSIZE file descriptors. Is it true that a 
theroretically infinite number of FDs can be opened by the server, and 
that I can handle > FD_SETSIZE connections by having some kind of linked 
list of fd_sets?

As an aside, the name of MUD, Multi-User Dungeon, was taken from the game 
Dungeon (Zork I, II, III). It was thought that Dungeon would define that 
type of game, and that all games of that type would thereafter be called 
Dungeons. This is not how it turned out, since Adventure (Colossal Cave) 
took the honour. Parts of Dungeon were based on Adventure, and the 
original version was written at MIT.

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