Does the stream device have the recived/send buffer?If yes,where does it define?

Hi All,
When I write the MC8051 program,there is buffer to recive or send the date
in the UART communication.And if there is date recived we can read the
buffer directly instead of reading the bit one by one according to the
timing graph.

However,Does the WinCE driver program have the same mechanism as MC8051? If
yes ,generally where is the buffer defined?Is it a register? For example,the
driver of the AC97
,...\WINCE420\PUBLIC\COMMON\OAK\DRIVERS\WAVEDEV\UNIFIED\ENSONIQ\

How does the chip read the media file and render?Is it one bit by one
bit,or read the buffer?

Thanks,
Peter