Suunto D5 has a circular memory with a capacity to save 400 dives. As the memory is circular, your 401st dive will replace your first dive, your 402nd dive will replace your second and so forth.
Note: Ensure you have DM5 version 1.3 or later installed on your computer to ensure that DM5 connects to your Suunto D5. DM5 will automatically notify you about available updates. If you don’t have DM5 yet, follow the link to download it.