Plug and play, except when it isn't.

Usually yes. Most modern systems will detect new RAM and run it at default speeds without any BIOS changes.

The exception is if you’re trying to run RAM faster than the JEDEC standard (like 3200MHz or higher), you’ll need to enable XMP (Intel) or DOCP/EXPO (AMD) in BIOS to get those advertised speeds. Without that, the RAM defaults to a conservative speed like 2133 or 2400MHz.

Also, if you’re mixing different RAM sticks or capacities, the system might downclock everything to the lowest common denominator. You can sometimes manually tune timings in BIOS, but that’s optional.

If you just swap the sticks and boot, it’ll work. You just might be leaving performance on the table. Check your BIOS once after installing to make sure the speed matches what you paid for.