Downloading dive computer to PC, . . . questions. .

[Eino Maki]

Happy New Year to All!
I have a Suunto dive computer that I have used one season. (started diving in Nov. 2002) The computer has recorded my first 19 dives and I have downloaded these onto my pc using the Suunto Dive Manager software. I think the computer has a memory that can hold about 30 dives.
#1.
Lets say I do dives 20 through 35. When I hit dives 31 through 35, do dives 1 through 5 sort of scroll their way out of the memory, into the ether?
#2.
When I get back home and want to download my 16 new dives, will the software automatically ad my new dives onto my existing file of my first 19 dives? Is there any danger that my first 19 dives will be overwritten by the new download?
I'm a rookie at this. Any help is appreciated.
Thanks!
Eino Maki