a method and apparatus for accessing data blocks in a computer system having multiple - disk drive rotational position sensing which is not centrally synchronized and where data read and write requests are normally weighted by the order of availability of requested data blocks . the weighting of the priority , or queue position , of selected data blocks is modified by advancing the apparent initial location of data blocks designated for preferental access and maintaining an availability signal , or peripheral interrupt , for an extended period . a special pre - data - transfer instruction indicates the duration of the peripheral interrupt . a circuit for implementing the invention has a storage register for receiving the special instruction , a down counter for decrementing for the duration of the designated pre - data - interrupt and an interrupt duration control latch for issuing and extinguishing the interrupt . the invention permits preferential processing of demand type high priority data where there is no central clock synchronization among peripheral storage devices .