To ensure compatibility when adding memory to a system with an existing DDR3 module, what should you do?

When adding memory to a system that already has an existing DDR3 module, checking the motherboard documentation for supported modules is essential. The motherboard documentation provides specific details about the types of memory that are compatible with the system, including specifications like speed (measured in MHz), voltage requirements, and supported capacities.

Different manufacturers may design memory modules that may appear physically similar but might not function properly together due to differences in timings or voltages. Additionally, the documentation will often list compatible memory modules and allow you to verify that any new purchase will work seamlessly with the currently installed RAM.

This careful approach ensures that the new memory will operate effectively within the existing system configuration, reducing the risk of errors or system instability that can arise from using incompatible or unsupported modules.