ESRI uses ArcGIS Server to create and publish its map cache (2D) and globe cache (3D) services for ArcGIS Online. ArcGIS Online map and globe services use server-side map caching and globe caching, meaning that predrawn images of the map or globe are stored on the server so that you can quickly request them through a URL. Cache services support high performance and scalability.
The tiling scheme includes the scale levels, point of origin, coordinate system, and image format of the cache tiles. These properties define where tile boundaries will exist and are important to match when overlaying caches in some clients. Other properties such as image format and antialiasing are also written into the tiling scheme. ArcGIS Server 9.3 makes it easier for you to choose to use the Google Maps/Bing Maps (formerly Microsoft Virtual Earth) or ArcGIS Online tiling scheme tiling scheme for your caches. These tiling schemes allow you to easily overlay your cache tiles with data from these online mapping services. ArcGIS Server 9.3 includes these tiling schemes as built-in options when loading a tiling scheme. See The tiling scheme section in the Choosing Cache Properties topic in ArcGIS Server 9.3 .NET Help for more information on the Google Maps/Bing Maps tiling scheme and the ArcGIS Online tiling scheme.
See also "Can I copy and share tile caches published by ESRI?"