There is built in a limit for how many simultaneous connections can be made by Windows. This limit can constraining when running a server like MySQL, FTP, HTTP, FileSharing etc. This limit can be changed in the registry with this STRING value:

[HKEY_LOCAL_MACHINE \System \CurrentControlSet \Services \VxD \MSTCP]
MaxConnections = "255" (Default = "100")

Note if using Win95 without having Winsock2 installed the datatype should be a DWORD.

Note that there is rumors that it cannot handle a limit beyond 300 connections, and some cannot even rise the value above 100.

More Info MS KB243116

Note if using an application that frequently opens and closes connections, then it might run out connections because after closing a connection, the connection is locked to make sure the other party has acknowledged that the connection is closed. To shorten the time (in seconds) the connection is locked:

[HKEY_LOCAL_MACHINE \System \CurrentControlSet \Services \VxD \MSTCP]
TcpTimedWaitDelay = "120" (Default = 240 secs)

Note if using an application that doesn't have a builtin keep alive mechanism, and relies on the TCPIP timeout checking (Every 2 hours). Then one might end up with connections that "never" closes. To shorten the interval between each TCPIP timeout check:

[HKEY_LOCAL_MACHINE \System \CurrentControlSet \Services \VxD \MSTCP]
KeepAliveTime = "1800000" (Default = 7,200,000 milisecs)

Related Configure TCPIP stack settings in Windows 9x