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In-Depth Information
cumulative growth rate for areal density for the last several years and 30% in
BPI over last one decade or so. Starting in the later part of 1990s, the track
density (TPI) has been growing at a rate faster than that of the growth in
linear density (BPI). Table 1.1 shows TPI and BPI of several products in the
fi
rst few years of this decade. It is evident that both the densities have been
increasing. However, the Bit Aspect Ratio (BAR) or the ratio between BPI
and TPI has been showing steady decrease during this period. This trend in
BAR suggests that the increase in track density is taking place at a rate higher
than that of linear density. Capability of sustaining the rate of increase in TPI
will play a more important role in pushing continuously the recording density
higher. Compared to the data shown here, the track density (20 TPI) and
linear density (100 BPI) of RAMAC were very small. It is generally believed
in the HDD industry that areal density still has a lot of room to grow, and it is
expected to reach 50 Terra bytes per squared inch in the future. The growth in
track density must be sustained at an appropriate rate to make this projection
a reality.
Ta
ble 1.1: Trend in track density, linear density, and bit aspect r
atio
Year
Company
Capacity
(GB)
kTPI kBPI BAR
2000
Maxtor
61.4
27.3
412
15.09
2000
IBM
40.0
35
415
11.86
2000
Maxtor
81.0
34
402
11.82
2000
Quantum
80.0
35.4
417
11.77
2000
Quantum
73.4
40
448
11.2
2001
Seagate
40.0
50
540
10.8
2001
Maxtor
15.0
46
489
10.63
2001
Maxtor
40.0
54
524
9.72
Hitachi
180.0
72
632
8.77
2003
Seagate
200.0
98
671
6.84
2004
Seagate
300.0
105
658
6.26
1.4.2 Trend in Drive Form Factor
Introducing a new form factor standard requires coordination between manu-
facturers of computers, producers of HDD, and other support industries that
produce components for HDD as well as for computers. There is a natural re-
sistance in the industry to changes in form factor unless there is a compelling
reason to do so. At the emergence of laptop computers, the HDD industry
created new, smaller drives to save space as well as power, a very important
consideration in the world of mobile computing. This was a necessity that the
HDD industry and other support industries eagerly acted to meet. There have
been only a few different form factors in the entire history of HDD. The most
