Typical performance bottlenecks in servers, as all know have 4 major factors.
Processor – Processes taking a long time to process or consuming a lot of processing power.
Disk – Disk performance issues due to bad disk style or low speed. Method of accessing a disc can also be a bottleneck.
Memory – Low memory resource or a program keeps up a huge portion of memory can also cause servers to work in a bad manner.
Network – Multiple paths on a network can cause bottleneck.
System Admin Guide 