Drupal has strong default caching systems, but the Boost module offers significant improvements.
Boost creates a cache in the file system rather than the database, so Drupal never needs to communicate with the database. This provides major a performance and scalability boost for sites that receiving mostly anonymous traffic (it doesn't help so much with logged-in users).
Boost isn't always this easiest module to set-up, but this video will help you get started.
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