Apache Reference: http_core, MaxClients
Maximum Number of Clients
Syntax: MaxClients A
Example: MaxClients 128
Since: Apache 1.0
This directive limits the number of simultaneous HTTP
requests that can be supported; no more than this number of
child server processes will be created. To configure more than
256 clients, one must edit the HARD_SERVER_LIMIT entry in
httpd.h and recompile Apache. Any connection attempts that exceed
the MaxClients limit will normally be queued in kernel space,
up to a number based on the ListenBacklog directive. Once a
child process is freed at the end of a different request, the
queued connection will be serviced.