Is this really possible?

Among the errands I ran today, my day off, was to get a new monitor for our computer. The original Dell one was never able to render a sharp image--it was murder on the eyes looking at its blurry smear.

Our computer is old (like 5-6 years) and is slow. Now, the computer seems to be really a lot faster. I am no electronics expert, but I just don't see how a monitor (running at a much higher resolution even) can speed up a computer! Even if the monitor driver is more efficient, how much cpu or memory was used for that? Couldn't be much I would think.