Caching systems are a crucial tool for scaling any application and increasing performance. They are something every Drupal site utilizes on some level, and while they are a critical component of your Drupal site, they can also be confusing to work with and when mis-configured can actually harm performance.

Aaron Welch from Cadre Web Hosting will explain in general what caching is, what it is used for, and cover some of the more common caching mechanisms out there, as well as how they work, the different types of problems they solve, how they interact, and when to use them. Included will be discussions of browser caches, local Drupal cache, opcode cache (APC, Eaccelerator), proxy caches like Varnish and Squid, memcache, and Content Delivery Networks.

Slides: 

caching demystified.pdf