Which is correct?
When compared ____ the high-performance computers of thirty years ago, current PCs seem like supercomputers.
Compare with and compare to are often used interchangeably and that use is not really wrong. If you’re comparing two things that are obviously similar, either to or with works fine.
However, a distinction can be made. Compare to is often used to stress similarities, especially between things that are, at first glance, dissimilar. For example, the computer is often compared to a human brain because of the way both process information. In this use, compare is synonymous with liken.
On the other hand, if you want to contrast two things, compare with is more useful. For example, when I compare my computer with my brain, I find my brain often slower to boot up (especially when it’s low on caffeine).
The Total Gadha GMAT blog provides a tip and quiz on compared to vs. compared with.
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