9.1 a. What is a device register? b. What is a device data register? c. What is a device status register?

(a) A device register is a register (or memory location) that is used for data transfer

to/from an input/output device. It provides a means of communication between the

processor and the input/output device. The processor can poll this register to find out

whether it has received an input or it can send an output from/to the specific device that the device register belongs to. In memory mapped I/O device registers are dedicated memory locations for each I/O device. There may be more than one device register (dedicated memory location) for one device.

(b) A device data register is a device register (a dedicated memory location in

memorymapped I/O) that holds the data that is to be input/output.

(c) A device status register is a device register (a dedicated memory location in

memorymapped I/O) that indicates the status of the input/output. It allows for the

processor to know whether or not input/output of the value in the device data register has occurred. Basically it is an important step to achieve synchronization in an asynchronous I/O system.

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