Task Manager tells you right away.

Open Task Manager (Ctrl+Shift+Esc), click “Performance” then “Memory.” If the total RAM matches what you installed, the OS sees it. On macOS, click the Apple menu > “About This Mac” — same deal.

It’s that simple. No third-party tools needed. If the number looks right, you’re done. If it’s less than expected, the stick might not be seated properly or your motherboard might not support that density.

BIOS sometimes shows the same info, but the OS is the final arbiter. It’s also the one that actually uses the memory, so trust it.

If the total doesn’t match, shut down, reseat the RAM, and check again. Usually fixes it.