in the old days you could get away with it
Wow. The exact opposite is my experience. In the old days, you had to go with the exact same manufacturer, size, model number, and even the same lot number or production run.
In the old days, packages of "dual channel" RAM contained RAM sticks that were actually individually tested at the factory, matched and paired for compatibility, then packaged together - and at a higher price too because of that special testing.
As I noted in that thread Layback Bear linked to,
Itaregid said:
Modern motherboards and CPU memory managers are much more capable of supporting mixed RAM than those of years ago. And modern RAM manufacturing techniques ensures RAM (from just about any maker) much more closely adheres to published specifications. So "in theory", you can mix and match brands to ensure compatibility as long as you buy RAM with compatible specifications. And in practice (again, with modern hardware), when you buy RAM with the same specifications as existing RAM, it does work's - most of the time.
But for your best odds to ensure total, trouble-free compatibility, I agree with LayBack Bear and recommend your new RAM either matches your old exactly, or you replace your old with all new.
I note today, the RAM in packages marketed as dual channel (or triple channel) are not individually tested and matched. They don't have to be because manufacturing techniques have improved so much in recent years that every stick of the same model coming off the production line (regardless of lot) match published specs within such tight tolerances, they don't need expensive, time consuming individual testing and matching.
They are packaged and sold as dual or triple as a convenience to consumers, and because it saves in logistics costs (packaging, shipping, inventorying, etc.). That's the only reason.
Now until Man can create perfection 100% of the time, there will always be exceptions. So to ensure compatibility, it is still best to buy the same brand and model number, when you can.
