Intel's 8237 DMA controller :
1) The 8237 contain 4 independent I/O channels
2) It contains 27 registers, 7 of which are system-wide registers and 5 for each channel.
3) Out of 5 register: 4 are 16-bit and 1 is 6-bit. they are
- DMA base address
- DMA current address
- DMA total
- DMA remaining
- 6-bit is the mode register