At the core of the SQL Server Database Engine are two major components: the Storage Engine and the Query Processor, also called the Relational Engine.
Storage Engine: takes care of reading data between the disk and memory in a manner that optimizes concurrency while maintaining data integrity
Query Processor: 1. takes care of devising a query plan (what algorithms/operators to implement) by Query Optimizer 2. execute the query according to that plan by Execution Engine