How can I check if my RAM is running in dual-channel mode before upgrading?

Download CPU-Z, open it, go to the Memory tab, and look for “Channel #” — it’ll say “Dual” or “Single.” Alternatively, open Task Manager (Ctrl+Shift+Esc), go to Performance > Memory, and check “Slots used” and “Form factor” in the bottom right. CPU-Z is more reliable. Also, most motherboards require sticks in slots 2 and 4 (or 1 and 3) for dual-channel.