Hardware Reference
In-Depth Information
3 milliseconds on high performance drives making spindle latency the most
signi
fi
cant contributor to the access time. Low access time is very important
in computer applications because the number of data transfers is so high that a
small increase in the time required for each transfer causes considerable overall
delays in processing data or running programs.
1.5 Alternative Recording Technologies
Hard disk drives are expected to maintain their position as the primary on-line,
non-volatile storage device for computing systems in the foreseeable future be-
cause of their advantages of large capacity with fast access but at low cost.
Though access time is faster in semiconductor memory, its higher cost per
stored bit makes it less attractive for mass storage. This is expected to be con-
tinued in the future. However, the semiconductor devices will have their usage
for low capacity functions such as on-board RAM and
fl
ash memory for small
and portable applications such as digital camera and MP3 player. The optical
storage devices cannot compete with hard drive technology in either storage
capacity or data access speed and will continue to
fi
ll the niche functions of
high capacity data portability and program distribution. The burgeoning mar-
ket segment of off-line storage will continue to grow providing better market
opportunities for high performance, quick access hard drive arrays. In addi-
tion, with the proliferation of consumer-oriented devices for which data storage
is a critical capability, non-computer applications are expected to contribute
signi
fi
cantly to future growth in overall disk drive demand.
There still exists wide opportunity for the amazing technological develop-
ment of hard drives to continue. Today's leading edge areal densities are close
to 100 gigabits per square inch. A consortium of industry, academic, and gov-
ernment participants (Information Storage Industry Consortium, NSIC) has
recently targeted 1000 gigabits per square inch for their new magnetic stor-
age demonstration development project. However, this effort to make the bit
size smaller and smaller is leading towards a situation which is constrained
by the super paramagnetic effect; the grains of the media becomes so small
that they interfere with one another and thus loose the ability to retain their
magnetic orientations. As a result, magnetic north and south poles of a grain
suddenly and spontaneously reverse corrupting the stored data and therefore,
making the storage device unreliable. Alternative technologies to overcome this
problem include perpendicular recording, heat assisted magnetic recording and
recording on patterned media.
Perpendicular Magnetic Recording:
At present, the HDDs employ Longitudinal recording which, as its name indi-
cates, aligns the data bits horizontally, parallel to the surface of the disk. In
