hi, are there more than on of DMA in computer or there is one for all devices? if so, why there is DMA SELECT in DMA organization? then , what is burst transfer? and why it is used with hard disk? lastly, cpu communicate with DMA to read and write from registers of DMA. I know cpu communicate with DMA to write no. of word in word count reg. and read it then ; as I know cpu write the address in address reg. of DMA and write control info. in control reg. of DMA , but I don't know why and when it read AR and control reg. of DMA? in block digram of DMA the lines for all registers of DMA are bidirectional. please , I need help in this topic. I appreciate any help. thanks in advance