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Polled I/O is a system by which the Operating System waits and monitors a device until the device is ready to read from. In early computer systems when a program would want to read a key from the keyboard, it would constantly poll the keyboard status port until a key was available; due to lack of multiple processes such computers could not do other operations whilst waiting for the keyboard. The solution and alternative to this approach is for the device controller to generate an interrupt when the device was ready to transfer data. The CPU handles this interrupt and the OS knows to fetch the data from the relevant device registers. This solution is called Interrupt-driven I/O.
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