Intel Xeon E5310
The slowest CPU in the 65nm Clovertown family. It is equipped with 4 cores that run at just 1.6GHz. It was cheaper but usually not the best option if you wanted decent performance for your end-users. The 2.33GHz and higher clocked parts offered snappier performance.
Because this CPU has the lowest multiplier available in this CPU-architecture it doesn't have EIST (Enhanced Intel Speedstep Technology) since it can't clock lower than multiplier 6x. EIST relies on lowering the multiplier (along with vCore) in order to reduce energy consumption.