What is the internal difference between LINQ-to-Objects and LINQ-to-Entities execution pipelines?

LINQ-to-Objects executes delegates in memory, while LINQ-to-Entities translates expression trees into SQL via EF provider.

LINQ-to-Objects operates on IEnumerable and uses compiled delegates executed directly by the CLR. LINQ-to-Entities operates on IQueryable and builds expression trees that are parsed by EF Core. The provider converts these expressions into SQL ASTs, optimizes them, and executes them on the database engine. The key architectural difference is execution location: CPU-bound iteration versus database-side execution.