The first major difference in In-Memory OLTP is the storage structure of both tables and indexes. The traditional storage engine in SQL Server was optimized for disk storage, especially for the block storage of hard disk subsystems. However, In-Memory OLTP was designed from the ground up to be memory resident, or memory optimized. This small, but important difference allowed a design with byte storage in mind. This means that memory-optimized tables avoid the needs of data pages and extents that we know from the normal, disk-optimized tables in SQL Server. Through this change, a significant overhead in page and extent management is removed. This reduction in overhead provides a major performance increase in itself.