What exactly is the difference between DVD-RW and DVD-RAM?

Can you use a DVD-RW in random access mode so it works like a hard drive? I think thats the advantage of DVD-RAM right?

I want to be able to use either DVD-RWs or DVD-RAMs to put videos I record from TV by normal letter access (With Easy DVD drag to disc) and I want to be able to delete any file and put a new file without having to format to get the space back that the old file used. Can DVD-RW do that or only DVD-RAM?

Thanks