PRML detection boosts hard-disk drive capacity

Over the past 10 years or so, the bit-capacity of mass-market hard-disk drives has increased 100-fold-the reward of improvements in read/write heads, magnetic materials, head-positioning systems, and much else. But as advances in those well-worn areas grow more costly and difficult, attention is turning to the read-channel electronics as a way to increase disk capacity and throughput rates in the future. More specifically, with the enormous advances made in mixed-signal semiconductor technology, it recently became practical to apply partial-response, maximum-likelihood (PRML) detection to low-cost drives. The key advantage of PRML is that it works with sequences of received data, rather than single bits, comparing data sequences and determining which one was most likely to have caused the observed signal. It is therefore more tolerant of intersymbol interference than pulse peak detection-today's most common read-channel technology.