1. Execution Timing: Middleware runs before the actual request reaches the runtime environment, modifying or passing the request to the runtime. In contrast, runtime executes during the request processing and is responsible for generating the final response.
2. Functionality: Middleware primarily focuses on request processing, such as authentication, logging, or modifying request/response objects. On the other hand, runtime is responsible for executing the application logic, including business operations and data processing.
3. Scope of Actions: Middleware operates at the request level, affecting how the request is handled by the application. In contrast, runtime operates at the application level, executing the core functionality of the application based on the incoming request.
4. Configuration: Middleware is typically configured at the application or server level, determining which middleware components to use and the order of execution. In comparison, runtime configuration consists of setting up environment variables, defining behaviors, and managing resources required for application execution.
5. Development Complexity: Implementing middleware involves writing code to intercept and modify requests, adding an additional layer of complexity to the application. On the other hand, runtime development focuses on writing the core application logic without the need for intermediary processing logic.
6. Performance Impact: Middleware can introduce overhead due to additional processing before reaching the runtime, potentially affecting the overall performance of the application. In contrast, runtime directly impacts application performance as it executes the main business logic, making it crucial for optimizing performance.

In Summary, Middleware and runtime differ in execution timing, functionality, scope of actions, configuration, development complexity, and performance impact in web applications.