Not what is stands for, but what it does.
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Memory is a place where your computer dumps all the data it is immediately using. When you build a brick in Blockland, this data goes into your RAM. When you save bricks, it goes into one drive or another. A common drive that you save things in is your hard drive. When your computer shuts off, all data is emptied from your RAM. I think that even when you exit a program, that specific data is removed from RAM. In short, your computer's RAM is it's short-term memory. RAM enables programs to be run faster than having to search through your hundred gigabytes of hard drive space used. If you are not using up all your RAM at one time, getting more will not help you reduce lag.