Controlling the BLOB
The third part of the caching trilogy covers the BLOB cache, or binary large object cache. In a typical site there are many references to CSS files and images. MOSS caches these objects to prevent multiple trips to the database for these resources. MOSS caches these resources on the Web-front end servers in the file system. This type of caching is not enabled by default.
To enable BLOB caching change the line in the Web.config file for the blobcache to true. You can set the maximum size for the cache in this line as well. The default is 10 GB. In the path attribute you can determine the file extensions that will be cached in this type of caching. You may want to add such file extensions as .swf for Flash movies, if your site utilizes them. NOTE: this caching only works on items that are in document libraries and lists. If you place files in the site but not in a library or list, the caching will not cache the file.
<BlobCache location="C:\blobCache" path="\.(gif|jpg|png|css|js)$" maxSize="10" max-age="86400" enabled="True"/>
You can also set the maxAge to the number of seconds that you want the client to retain the object in its cache. This allows the client to use its copy of the resource and not re-request the URL for the resource until the timeout has expired.
With these three types of caching your Internet facing MOSS site can efficiently serve up files to many users.
Additional resources for caching:
Eduardo Castro - http://comunidadwindows.org