What are the differences between Selenium RC and Selenium Web driver?

Selenium RC and WebDriver diifer in the middle layer technology. RC uses a javascript function to assis the testing of web pages while WebDriver uses the in-build functions of the browser for tetsing the web pages.

what is the difference between selenium IDE and selenium grid?

• selenium RC is slower than web driver because of simple architecture.
• web driver directly interacts with browser in case of selenium RC, RC server should must to do so..
• web driver's API(Application Programming Interface) is more clearly gives information than selenium RC..
• web driver will support HTML but Selenium RC  cannot support..