Hardware Reference
In-Depth Information
sq.inchinthe1956RAMAC(5MBofstorageonfifty24-inchplatters)tobeyond500Gb/
sq. inch in 3TB drives in 2010.
Current drives have used perpendicular recording techniques to go well past what was
previously considered the point at which the superparamagnetic effect takes place. This is
an effect in which the magnetic domains become so small that they are intrinsically un-
stable at room temperature. Techniques such as perpendicular recording combined with
extremely high coercivity media are being employed to enable future magnetic storage
densitiesofupto1000Gb/sq.inchormore,butbeyondthat,scientistsandengineersmight
have to look toward other technologies. One such technology being considered for the fu-
ture is patterned media, in which a disk is preformatted with magnetic domains that can
be more tightly packed without interfering with each other. Another possible future tech-
nologyisholographicstorage,inwhichalaserwritesdatathree-dimensionallyinacrystal
plate or cube.
Figure 8.13
shows how areal density has increased by a factor of more than 200 million
times from when magnetic storage was developed (1956 RAMAC) to the present.
Figure 8.13
Evolution of areal density in magnetic disk storage.
To increase areal density while maintaining the same external drive form factors, drive
manufacturers have developed media and head technologies to support these higher areal
