Hardware Reference
In-Depth Information
In the early 1960s, HDD recording heads operated at floating heights as large as 200 μ-
inches to 300 μ-inches; today's drive heads are designed to float as low as 10nm (nano-
meters)or0.4μμ-inchesabovethesurfaceofthedisk.Tosupporthigherdensitiesinfuture
drives,thephysicalseparationbetweentheheadanddiskisexpectedtodropevenfurther,
such that on some drives there will even be contact with the platter surface. New media
and head designs will be required to make full or partial contact recording possible.
Caution
The small size of the gap between the platters and the heads is why you should never open
the disk drive's HDA except in a clean-room environment. Any particle of dust or dirt that
gets into this mechanism could cause the heads to read improperly or possibly even to strike
the platters while the drive is running at full speed. The latter event could scratch the platter
or the head, causing permanent damage.
To ensure the cleanliness of the interior of the drive, the HDA is assembled in a class-100
or better clean room. This specification means that a cubic foot of air can't contain more
than 100 particles that measure up to 0.5 microns (19.7 μ-inches). A single person breath-
ing while standing motionless spews out 500 such particles in a single minute! These
rooms contain special air-filtration systems that continuously evacuate and refresh the air.
A drive's HDA should not be opened unless it is inside such a room.
Althoughmaintaining aclean-roomenvironmentmightseemtobeexpensive,manycom-
panies manufacture tabletop or bench-size clean rooms that sell for only a few thousand
dollars. Some of these devices operate like a glove box; the operator first inserts the drive
and any tools required, closes the box, and then turns on the filtration system. Inside the
box, a clean-room environment is maintained, and a technician can use the built-in gloves
to work on the drive.
In other clean-room variations, the operator stands at a bench where a forced-air curtain
maintainsacleanenvironmentonthebenchtop.Thetechniciancanwalkinandoutofthe
clean-room field by walking through the air curtain. This air curtain is similar to the cur-
tain ofair used in some stores and warehouses to prevent heat from escaping in the winter
while leaving a passage wide open.
Because the clean environment is expensive to produce, few companies except those that
manufacture the drives are properly equipped to service HDDs.
Read/Write Head Designs
As disk drive technology has evolved, so has the design of the read/write head. The earliest
heads were simple iron cores with coil windings (electromagnets). By today's standards, the
original head designs were physically enormous and operated at low recording densities.
