What is the difference having 4 ram slot on a 2 ram slot motherboard ...
Most consumer-grade motherboards come with four RAM slots; the main goal of these RAM slots is to connect the CPU to the RAM sticks using the motherboard ...
Ram Sticks
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How to add RAM slots from the outside to a laptop
For example, if you have two RAM sticks and four slots, you typically need to install the sticks in slots 1 and 3 or slots 2 and 4 to enable dual-channel mode.