|Ram that works in another mboard , or any ram you buy or have lying around, may not work properly, or sometimes, not at all - even if it physically fits and is the right overall type (e.g. SDram, DDR, DDR2, etc.; PCxxxx, xxx mhz) for your mboard. In the worst cases of incompatibilty your mboard WILL NOT BOOT all the way with it installed, and the mboard may not even beep - the ram has to be compatible with the mboard's main chipset, or in the case of recent mboards, compatible with the memory controller built into the cpu.|
In some cases individual modules will work fine in any ram slot, but when you install more than one they are not recognized properly, either because they are not 100% compatible, or because they are specified to use different voltages and the ram that needs the higher voltage is not recognized properly.
See response 5 in this for some info about ram compatibilty, and some places where you can find out what will work in your mboard for sure:
Correction to that:
Once you know which module ID strings (part numbers) work in your mboard, you can get them from anywhere you like that has ram with those ID strings.
If you have brand name ram, it is usually easy to look up whether it's ID string (part number) is in a list of compatible modules found by using your mboard or brand name system model number.
If the ram is generic, that may be difficult or impossible.
Some ram manufacturer's modules do not strictly adhere to the JEDEC standards that most mboards bioses use to determine ram settings.
In that case, the ram settings in the bios Setup that the bios has automatically chosen may not be correct.
Check the ram settings in your bios - the ram voltage, and the ram timing numbers - those should be the same as for the specs for the modules themselves. Often the ram voltage and timing numbers are printed on the label on the modules.
If the voltage setting or timings settings in the bios are different from the specs for the ram, change them in the bios. The timing numbers must be as close as you can get to the same, or slower timings (higher numbers = slower) - you won't notice the difference the slower settings make.
If you have a mix of different modules
- don't mix ram that different voltages are specified for - the bios will force the ram to use the lowest voltage, if "by spd" or similar is used (default settings) - ram that a higher voltage is specified for is more likely to not work properly in that situation.
- the bios settings must be those for the slowest timing settings of all the modules, or slower (higher numbers = slower).
You MAY be able to custom set the ram voltage to the higher ram voltage in the bios if you do NOT have the bios set to detect the ram "by SPD" or similar, however, you must NOT exceed the max voltage range for the modules that require a lower voltage, and that can be hard to determine, unless you can find detailed specs - e.g. if the ram is Kingston ram that doesn't have a brand name system specific part number, that info is easily found.