PC Hardware in a Nutshell, 3rd Edition

... When You Are Adding Memory

If you experience problems when adding memory, note the following:

• If a DIMM appears not to fit, there’s good reason. SDR-SDRAM DIMMs have two notches whose placement specifies 3.3V versus 5V and buffered versus unbuffered. DDR-SDRAM DIMMs have a keying notch in a different location. If the DIMM notches don’t match the socket protrusions, the DIMM is of the wrong type.

• If the system displays a memory mismatch error the first time you restart, that usually indicates no real problem. Follow the prompts to enter Setup, select Save and Exit, and restart the system. The system should then recognize the new memory. Some systems require these extra steps to update CMOS.

• Verify the modules are installed in the proper order. Unless the motherboard documentation says otherwise, fill banks sequentially from lowest number to highest. Generally, install the largest module in Bank 0, the next largest in Bank 1, and so on. A few systems require the smallest module be in Bank 0 and larger modules sequentially in higher banks.

• If the system recognizes a newly installed module as half actual size and that module has chips on both sides, the system may recognize only single-banked or single-sided modules. Some systems limit the total number of “sides” that are recognized, so if you have some existing smaller modules installed, try removing them. The system may then recognize the double-side modules. If it doesn’t, return those modules and replace them with single-sided modules. ...