Patent ID: RE39809

Claim:
In a rotating disk data storage device of the type including a disk whereon data is written by a transducer head adjacent the disk in angularly extending sectors on concentric data tracks to be subsequently read therefrom by the transducer; a controller responsive to sector location pulses for locating said sectors; and means for moving the transducer head between tracks on the disk; an apparatus for providing the sector location pulses, comprising: master clock means synchronized with the rotation rate of the disk for providing master clock signals indicative of the angular location of the transducer head with respect to a selected index location on the disk following passage of the index location by the transducer head; a first counter clocked by the clock means; latch means for storing a selected time corresponding to a selected angular distance along a selected track on the disk; an accumulator connected to the latch means for adding said selected time to the contents of the accumulator each time the accumulator is clocked by an accumulator clock signal; a first comparator connected to the first counter and the accumulator for providing an electrical indication that the contents of the counter is at least as large as the contents of the accumulator; accumulator clock means connected to the first comparator and responsive to said electrical indication for repetitively providing the accumulator clock signal to the accumulator so long as the accumulator contents does not exceed the first counter contents; master reset means for resetting the first counter and the accumulator at such times that the index location on the disk passes the transducer head; partial reset means for entering the selected time into the latch means and resetting the accumulator each time the transducer head is moved to a new track on the disk; and sector location pulse generation means, connected to the first comparator, for providing the sector location pulses to the controller in response to at least selected ones of said electrical indications that the contents of the first counter is at least as large as the contents of the accumulator.