On-Die Termination

Common Options : 50 Ohms, 75 Ohms, 150 Ohms (DDR2) / 40 Ohms, 60 Ohms, 120 Ohms (DDR3)

Quick Review

The On-Die Termination BIOS option controls the impedance value of the DDR2 / DDR3 on-die termination resistors. DDR2 modules support impedance values of 50 ohms, 75 ohms and 150 ohms, while DDR3 modules support lower impedance values of 40 ohms, 60 ohms and 120 ohms.

A lower impedance value improves the resistor's ability to absorb signal reflections and thus improve signal quality. However, this comes at the expense of a smaller voltage swing for the signal and higher power consumption.

The proper amount of impedence depends on the memory type and the number of DIMMs used. Therefore, it is best to contact the memory manufacturer to find out the optimal amount of impedance for the particular set of memory modules. If you are unable to obtain that information, you can also follow these guidelines from a Samsung case study on the On-Die Termination of DDR2 memory :

• Single memory module / channel : 150 ohms
• Two memory modules / channels
  • DDR2-400 / 533 memory : 75 ohms
  • DDR2-667 / 800 memory : 50 ohms

Unfortunately, they did not perform any case study on the On-Die Termination of DDR3 memory. As such, the best thing to do if you are using DDR3 memory is to try using a low impedance of 40 ohm and adjust upwards if you face any stability issues.