Hardware Reference
In-Depth Information
Table 1.2: Dimensions in drives of different form factors
Form
factor
Length
(in)
Width
(in)
Height
(in)
Comments
5
4
inch
8.0
5.75
3.25
Ful l
Height
Early 1980
8.0
5.75
1.63
Half
Height
Early 1980-90
8.0
5.75
1.00
Low
Pro
fi
le
mid to late 1990
8.0
5.75
0.75-0.8
mid to late 1990
Ultra
Low
Pro
fi
le
3
2
inch
5.75
4.0
1.63
Half
Height
Low
Pro
fi
le
5.75
4.0
1.0
most common
form factor
for
PC
2
2
inch
3.94
2.75
0.75
19 mm
height
for Laptop
3.94
2.75
0.67
17 mm
height
for Laptop
3.94
2.75
0.49
12.5 mm
height
for small Laptop
3.94
2.75
0.37
9.5 mm
height
for
very
small
Laptop
1.3inch
Kittyhawk
3.37
2.13
5mm or
10.5mm
1992, didn't sur-
vive
1.0inch
Micro
drive
1.6
1.43
5mm
1998
4,500, 5,400, 7,200, 10,000, to now 15,000 RPM hard drives. This has posed
challenges to keeping the windage off-track disturbances to an acceptable level.
Fluid dynamic bearings have replaced ball bearing spindles to reduce runout
(off-track movement of the head or disk) at high RPM. The higher data rates
coming into the head due to the higher rotational speed and bit density have
introduced challenges in drive electronics to be able to reliably process the
data.
The time required to move the head to a new track position and get it ready
for reading or writing is called access time. It is the sum of the time required
to
fi
nd the new track (seek time), time required to settle on it (settling time),
and latency. Latency is de
fi
ned as half of the time the disk takes to make one
rotation as, on the average, the desired data is located 180
◦
from the position
where the head settles onto the track. One-third stroke seek times are around
