Magnetic Storage Principles - Upgrading and Repairing PCs - page 538

A Femto slider has three distinct areas with complex shapes designed to achieve a con-
sistent head-to-disk floating height across the disk as well as minimal height loss under
high-altitude (low-pressure) conditions. The shallow etch area creates a stepped air inlet
allowing airflow to create a positive pressure under the air-bearing surface that lifts the
sliderawayfromthedisk.Thedeepetchareacreatesanoppositenegativepressurepocket
that simultaneously pulls the slider closer to the disk surface. The combination of positive
and negative pressures is designed to balance the force of the suspension arm pushing the
slider toward the disk, while keeping the slider at the desired floating height away from
the disk surface. The balance of positive and negative pressures stabilizes and reduces the
floatingheightvariationscommonlyfoundinoldersliderdesigns.Thefirstdriveusingthe
Femto slider design was the Hitachi 7K6021/2-inch drive released inMay2003.Most of
the higher-capacity drives on the market today use this design.
Data-Encoding Schemes
Magnetic storage is essentially an analog medium. The data a PC stores on it, however,
is digital information—that is, 1s and 0s. When the drive sends digital information to a
magnetic recording head, the head creates magnetic domains on the storage medium with
specific polarities corresponding to the positive and negative voltages the drive applies to
the head. The flux reversals form the boundaries between the areas of positive and neg-
ative polarity that the drive controller uses to encode the digital data onto the analog me-
dium. During a read operation, each flux reversal the drive detects generates a positive or
negative pulse that the device uses to reconstruct the original binary data.
Tooptimizetheplacementoffluxtransitionsduringmagneticstorage,thedrivepassesthe
rawdigitalinputdatathroughadevicecalledan encoder/decoder (endec) ,whichconverts
the raw binary information to a waveform designed to optimally place the flux transitions
(pulses) on the media. During a read operation, the endec reverses the process and de-