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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Performance, Quality and Reliability | Hard Disk Performance | Hard Disk Performance Specifications | Other Performance Specifications ]

Power Consumption

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


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