IIS 8 on Windows Server 2012 doesn’t have any fixed concurrent request limit, apart from whatever limit would be reached when resources are maxed.
However, the client version of IIS 8, which is on Windows 8, does have a concurrent connection request limitation to limit high traffic production uses on a client edition of Windows.
Source : Windows 8 / IIS 8 Concurrent Requests Limit - Scott Forsyth's Blog
