1. In a data processing system, means for providing automatic polling of a peripheral in response to digitally coded input/output descriptors comprising: a system memory for storing a read-from-peripheral digitally coded input/output descriptor and a write-to-peripheral digitally coded input/output descriptor, each including a settable poll indication, said write-to-peripheral descriptor also including a linking address to said read-from-peripheral descriptor, and said read-from-peripheral descriptor also including a linking address to said write-to-peripheral descriptor, said write-to-peripheral descriptor additionally including poll message addresses of a plurality of poll messages stored in said memory, and further including a pointer address pointing to a particular one of said poll message addresses; and input/output control means for controlling the transfer of data between said memory and said peripheral; said input/output control means including means for fetching said write-to-peripheral descriptor from said memory and in response to the detection of a predetermined setting of the poll indication of the fetched write-to-peripheral descriptor causing the poll message pointed to by the pointer address to be transferred to said peripheral following which the pointer address is modified to point to another poll message; said input/output control means also including means for automatically fetching said read-from-peripheral descriptor from said memory in response to the linking address of the fetched write-to-peripheral descriptor and for executing the fetched read-from-peripheral descriptor so as to provide for the transfer from said peripheral of a response to the poll message transferred thereto during execution of said write-to-peripheral descriptor; said input/output control means additionally including means for automatically linking back from said read-from-peripheral descriptor to said write-to-peripheral descriptor using the linking address of said read-from-peripheral descriptor so as to provide for another execution of said write-to-peripheral descriptor, said linking back occurring in response to a predetermined setting of the poll indication of said read-from-peripheral descriptor and the receipt of a first predetermined type of response from said peripheral to the poll message transferred thereto during execution of the immediately preceding write-to-peripheral descriptor.