What is the function of CD rw driver?

you must be confused. A CD-RW is a compact disk that, when put into a special drive, can have data written to it. Because it is rewritable (RW) the disk can have new data written over the old. A driver is a set of instructions that tells your operating system (eg Windows XP, MAC OSX, Windows Vista) how to interact with a specific type of hardware (eg a printer, network card, or hard drive). As you can see, the phrasing of your question does no make any sense-- I'm guessing you've misread something or are confusing terminology.