Barracuda 4LP Product Manual, Rev. D
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During a prefetch operation, the drive crosses a cylinder boundary to fetch more data only if the Discontinuity
(DISC) bit is set to one in bit 4 of byte 2 of Mode parameters page 08h.
Whenever prefetch (read look-ahead) is enabled (enabled by DRA = 0), it operates under the control of ARLA
(Adaptive Read Look-Ahead). If the host uses software interleave, ARLA enables prefetch of contiguous blocks
from the disc when it senses that a prefetch “hit” will likely occur, even if two consecutive read operations were
not for physically contiguous blocks of data (e.g. “software interleave”). ARLA disables prefetch when it decides
that a prefetch “hit” will not likely occur. If the host is not using software interleave, and if two sequential read
operations are not for contiguous blocks of data, ARLA disables prefetch, but as long as sequential read oper-
ations request contiguous blocks of data, ARLA keeps prefetch enabled.
