If you do run MyBB on a Windows Server with the built-in IIS webserver you might notice that MyBB is slower on IIS installations than on Apache.
The reason is in the database connection of the default installation of MyBB. The default value for the database server is localhost which is correct for most installations. On IIS, setting localhost as database server will cause a DNS lookup in the system. This DNS lookup takes some time and slows down your MyBB on every single database connection start.
The lookup can be prevented which saves you up to two seconds on each pageload if you do not set localhost as database server but use the IP of the database server. In most cases, you’ll have the database on the same – local – server and the IP will be 127.0.0.1.