Patent ID: 6292912
Filing Date: 2001-09-18
Classification: G06F,G11B

Abstract:
A disk drive having a normal mode of operation and a built-in self-test mode of operation for producing a sequence of channel metrics {.GAMMA..sub.n }, the disk drive comprising:a recording surface having a plurality of bit cells;a transducer for reading the plurality of bit cells to produce a noise-corrupted read signal;means responsive to the noise-corrupted read signal for generating a sequence of observed samples {y.sub.n }, the sequence of observed-samples {y.sub.n } forming a sequence of observed-sample sequences {Y.sub.n }, each observed sample sequence Y.sub.n having an earliest observed sample and a latest observed sample;means operative during the built-in self-test mode of operation for providing a sequence of expected samples {w.sub.n }, the sequence of expected samples forming a sequence of expected-sample subsequences {W.sub.n }, each expected-sample subsequence W.sub.n having an earliest expected sample and a latest expected sample;computation means for computing a sequence of channel metrics {.GAMMA..sub.n }, each channel metric .GAMMA..sub.n being a function of a distance determined from one of the observed-sample subsequences Y.sub.n to the corresponding expected-sample sequence W.sub.n, each channel metric .GAMMA..sub.n being independent of the earliest observed sample in every prior observed-sample subsequence Y.sub.n and the earliest expected sample in every prior expected-sample subsequence W.sub.n ;means for computing a mean .mu..sub..GAMMA. of the channel metrics .GAMMA..sub.n ;means for computing a standard deviation .sigma..sub..GAMMA. of the channel metrics .GAMMA..sub.n ; andmeans for computing a ratio of the mean .mu..sub..GAMMA. to the standard deviation .sigma..sub..GAMMA., the ratio (.mu..sub..GAMMA. /.sigma..sub..GAMMA.) corresponding to a signal to noise ratio.