The WebSphere eXtreme Scale licensed program is an elastic, scalable, in-memory data grid. The data grid dynamically caches, partitions, replicates, and manages application data and business logic across multiple servers. WebSphere eXtreme Scale performs massive volumes of transaction processing with high efficiency and linear scalability. With WebSphere eXtreme Scale, users can also get qualities of service such as transactional integrity, high availability, and predictable response times. WebSphere eXtreme Scale can be used in different ways. Users can use the product as a very powerful cache, as an in-memory database processing space to manage application state, or to build Extreme Transaction Processing (XTP) applications. These XTP capabilities include an application infrastructure to support users most demanding business-critical applications. WebSphere eXtreme Scale has servers, called container servers, that provide its in-memory data grid. These servers can run inside WebSphere Application Server, or on simple Java Standard Edition (J2SE) Java virtual machines. More than one container server can run on a single physical server. As a result, the in-memory data grid can be large. The data grid is not limited by, and does not have an impact on, the memory or address space of the application or the application server. The memory can be the sum of the memory of several hundred, or thousand, Java virtual machines, running on many different physical servers. WebSphere eXtreme Scale offers a number of data grid configurations, from a single, simple local cache, to a large distributed cache, using multiple Java virtual machines or servers. WebSphere eXtreme Scale also supports an EntityManager programming interface for storing entities in the cache. This programming interface is like entities in Java Enterprise Edition.