One of the benefits of
RAM over hard drive, is that reading and writing to a hard drive is an electrocal/mechanical operaton. Whereas, the same operation to
RAM is solely electrical. This makes the operation extremely faster. When the available
RAM space is filled, Windows uses available space on the hard drive. The more
RAM you have the less Wndows has to read/write to the hard drive. Your
CPU and Windows will dictate how much
RAM can be installed.
Also, the hard drive surface is subject to wearing out (going bad) to a much greater degree than
RAM is.
Hope that helps.