Is it safe to mix different brands and speeds of RAM?

Mixing RAM brands is usually fine, but mixing speeds is risky. Different brands with the same speed, timings, and voltage work well. Mixing speeds forces the faster stick to slow down to match the slower one, which is stable but not ideal. The real gamble is mixing different timings like CL16 vs CL18, which can cause instability or hurt performance. If you already have mismatched sticks, test with MemTest86 or run memory-heavy tasks—if it works, fine; if not, buy a matched kit.