CCOVICH - the hard drive (as outlined above) is for storing files. RAM is for processing those files. If you don't do anything with the files then they sit there and have no impact on performance. If you read/write those files constantly then there is an impact on performance.
A real world equivalent would be to imagine your hard drive as a filing cabinet. You (combination of RAM/CPU and a whole host of other things, but RAM for these purposes) go looking for a file in a small filing cabinet and it takes you a few seconds. Then you have to put the file down and go look for another. Put that down and go looking for another, etc . . .
Now imagine instead of a single filing cabinet you are looking in a warehouse full of filing cabinets. It will take a lot longer to find each file. In the hard drive world this is speeded up somewhat by other elements like caching and indexing but the analogy holds pretty true.
If you have a warehouse full of filing cabinets you can access a whole series of files a whole lot faster if you have more people going looking for the files at the same time. This is the equivalent of adding more RAM when accessing a large hard drive.
Of course, if 99% the warehouse full of files isn't accessed then having all these extra people isn't going to add a whole lot to the experience since they will be twiddling their thumbs most of the time.
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