We are no longer supporting APC on our servers because of stability issues. Please consider using Memcached (recommended) or XCache instead.
By default, Magento stores the cache on the file system. This is not optimized for performance as disk IO is usually a large bottleneck in any server, even with faster SSD disks. A solution is to use APC (Alternative PHP Cache) to store the Magento cache in memory (RAM) instead, which is going to be a lot faster. Fortunately, Magento has built-in support for APC so all that is needed to make it work is a little configuration change.
To use APC as a fast backend cache, simply add the following to your app/etc/local.xml
with a unique identifier to your store, such as the domain name.
Then flush your current cache and enjoy the speed improvement!