What is the difference between a buffered I/O (BIO) and a direct I/O (DIO)?

A.
The user must provide a buffer to perform a BIO, but not for a DIO.

B.
BIOs are substantially faster than DIOs, but consume more memory.

C.
BIO data is copied to/from a system buffer before/after performing the I/O.

D.
Most I/Os to terminals are DIOs; all I/Os to disks are BIOs.