Abstract: Phase discrimination and data separation method and apparatus for on-track error recovery by shifting input data in time relative to a clock to improve recovery of error bits due to bit shift in a disk storage system having a servo clock syncronized to a disk's rotational speed and a refernce clock which must be synchronized to the servo clock to insure that the data previously written onto the disk will be retrieved correctly during read back. Data encoded in (1,7) or denser codes can be recovered because of fewer transitions in a phase discriminator and therefore a shortened phase discrimination cycle in a feedback loop to avoid interference into the following correction. Readback data pulses for address mark (AM) search operations are standardized while a PLL is phase locked to the servo data, reducing or eliminating misdetection of AM due to delay skew or pulse width variations. Sequential logic avoids race conditions.

Abstract: A system for controllably varying the width of the data window in a magnetic storage device to perform comparative data detection error rate measurements thereon is provided. The system generates the programmably and continuously variable stressed data window symmetrically within, and in locked phase with, the full data window under the control of a single current DAC in the VCO of the device.