Persistent Object Cache
One of the big recent additions is the Persistent Object Cache. Objects such as pages, categories, options, and users are saved locally to disk so that WP doesn’t have to make a trip to the database. The object cache is completely pluggable, allowing hosts to tailor the cache to their particular usage and needs. Folks on the hackers and testers lists have been shaking out the bugs. The cache is looking pretty stable as of now.