There are several reasons why power consumption is an area of concern for PC users. The
first is that the amount of power needed by the hard disks must be provided for when specifying the power supply (although
modern systems with one hard disk don't generally need to worry about this). The second is
that the start-up power requirements
of hard disks exceed their normal requirements and must be given special consideration in
systems with multiple storage drives. The third is that more power consumption, all else
being equal, equates to more heat dissipated by the drive. The final one is environmental:
the trend is towards systems that use less power just for the sake of using less power!
The power consumption specifications provided for a drive vary from manufacturer to
manufacturer. Some provide only a "typical" rating for the drive during average
conditions, a start-up peak value for the +12 V voltage, and that's it. Others provide a
comprehensive look at the drive's use of both +5 V and +12 V power under various
conditions. For example, the table below contains the power consumption specifications for
the IBM Deskstar 75GXP, four-and five platter models. Note that unlike most hard disk
specifications, power consumption normally is higher for drives with more platters even
within the same family--since they have more mass to move, more power is required to turn
the platters. Many manufacturers just quote an average for the whole family, but IBM
generally doesn't:
Operating
Condition |
+5 V draw (Amps, RMS) |
+12 V draw (Amps,
RMS) |
Power Consumption
(W) |
Start-Up |
Peak |
0.81 |
1.81 |
-- |
Random
R/W Operation |
Peak |
1.02 |
2.23 |
-- |
Average |
0.41 |
0.78 |
11.5 |
Seek |
Peak |
0.47 |
2.23 |
-- |
Average |
0.27 |
0.84 |
11.4 |
Idle |
Average |
0.24 |
0.57 |
8.1 |
Standby |
Average |
0.26 |
0.015 |
1.5 |
Sleep |
Average |
0.17 |
0.015 |
1.0 |
Examining these numbers reveals a number of facts about how the drive uses power.
First, notice that when operating (platters spinning and actuator moving), the +12 V draw
is about 0.8 A; when idle (platters spinning but actuator stationary), it is about 0.6 A;
and when in standby (platters stationary), +12 V is about zero. This tells you that
roughly 3/4 of the +12 V power is taken by the spindle motor and roughly 1/4 by the
actuator assembly. +5 V is primarily used to drive the controller's components, which is
why even in standby mode a fair percentage of the +5 V power required during operation.is
needed. This is typical of modern drives. "Real-world" power consumption will
generally be close to what the manufacturer specifies, but bear in mind that actual
consumption will depend on a number of factors, most especially the manner in which the
drive is used.
Power consumption is primarily affected by the design of the drive's spindle motor and the number and size of the spindle platters, and to a
lesser extent, other components such as the actuator
and controller board.
Next: Hard
Disk Internal Performance Factors
