An Operating Systems Vade Mecum

The device interface 159processeskerneldevice drivermainstoreDMAstatuscontrollerordersinterruptsdevicedevicedeviceFigure 5.6 DMA2.3 ChannelsSometimes controllers are themselves connected not to device registers but rather to achannel, also known as an IOP, for ‘‘input/output processor.’’ Figure 5.7 shows how achannel is connected. The purpose of the channel is to provide some amount of devicetransparency to the cpu. Channels are subsidiary cpu’s that use a different machineprocesseskerneldevice drivermainstorechannelprogramDMAstartchannelinterruptscontrollercontrollerdevicescontrollerFigure 5.7 Devices connected through a channel