Symptoms
- System works most of the time but crashes occasionally under load
- RAM sticks are different brands, capacities, or speeds
- BIOS shows the RAM running at a lower speed than one of the sticks is rated for
- Problem appeared after adding a second kit of RAM to an existing one
Likely causes
- CommonDifferent RAM speeds forcing the system to run at the slower stick's speed, sometimes unstablyMotherboards typically run all RAM at the speed of the slowest stick, but not always cleanly.
- CommonMismatched timings between different RAM kitsEven at the same speed, differing timings can create instability.
- PossibleTotal RAM configuration not officially supported by the motherboardSome boards have specific supported configurations for four sticks vs. two.
- PossibleOne of the mismatched sticks is simply lower quality or borderline faultyInstability may trace back to one specific stick rather than the mismatch itself.
What to do
- Check each stick's rated speed and timings, either printed on the label or via a tool like CPU-Z.
- In BIOS, manually set the RAM speed and timings to match the slower/more conservative stick's rated specs.
- If instability continues, test with only one kit installed at a time to see if one specific kit is the problem.
- Check the motherboard's supported memory list for whether your combined configuration is validated.
- As a longer-term fix, consider replacing mismatched kits with a single matched kit of the needed total capacity.
- Run a memory test (like MemTest86) after making changes to confirm stability.
Tools and parts
- CPU-Z or similar system info tool
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.