An apparatus including first and second reservation stations. The first
reservation station dispatches a load micro instruction, and indicates on a hold
bus if the load micro instruction is a
specified load micro instruction directed to retrieve an
operand from a prescribed resource other than on-core cache memory. The second
reservation station is coupled to the hold
bus, and dispatches one or more younger micro instructions therein that depend on the load micro instruction for execution after a number of
clock cycles following dispatch of the first load micro instruction, and if it is indicated on the hold
bus that the load micro instruction is the
specified load micro instruction, the second
reservation station is configured to stall dispatch of the one or more younger micro instructions until the load micro instruction has retrieved the
operand. The resources include an input / output (I / O) unit, configured to perform I / O operations via an I / O bus
coupling an out-of-order processor to I / O resources.