On-the-fly splitting of disk data blocks using timed sampling of a data position indicator

摘要

A disk in a disk drive has radial spokes wherein servo bursts are recorded, and multiple concentric bands holding data blocks in pre- defined block frames. To maximize data density, the data rate in each band is proportional to the band radius, and the ratio of block frames to spokes in a given band may be non-integral. In such bands, some data blocks are split by a spoke. A disk controller in the disk drive uses a byte position accumulator (BPA) when splitting a data block. During the transfer of a data block, the BPA counts at the nominal data transfer rate to continually identify by its position in the data block a byte therein to be transferred shortly. The BPA output feeds a latch which is normally open to receive the BPA output. A timer within the disk controller establishes the rotational time at which the data transfer must be suspended to avoid a spoke. The timer generates an early warning signal in advance of this time which closes the latch. The value in the closed latch is the position of the last data byte to be transferred before the split. A comparator indicates when a count of bytes transferred has reached the value in the latch; the data transfer is then suspended until the spoke has passed.