Plug and Play is a technology wherein hardware components that are installed on PCs using Microsoft operating system are immediately recognized and made usable. This means that the drivers necessary to make it work are already available on the operating system package.
Standard modules contain variables, procedures and functions that are accessible anywhere within the project. A class module contains properties and events, and is made accessible only by objects that were created as an instance of that class.
RDO is Hierarchy model where as ADO is Object model. ADO can access data from both flat files as well as the data bases. I.e., It is encapsulation of DAO, RDO , OLE that is why we call it as OLE-DB Technology.