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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 Internal Performance Factors | Mechanical Design Factors ]

Actuator Characteristics

The hard disk's actuator--or more correctly, its actuator assembly, comprising the actuator, head arms, head sliders and read/write heads--is one of the most important performance-limiting components in the hard disk. It's also one of the least-discussed and least-understood; I discuss it in detail in this operation section.

The primary impact that the actuator assembly has is on positioning performance. Since random accesses require the heads to move over the surface of the disk to the correct location, and the actuator controls this process, the actuator assembly is the primary influence on the drive's seek time. Seek time in turn is the largest component of access time. In order to improve performance, manufacturers are constantly striving to reduce seek times by improving the speed of the actuator assembly. The first step taken was to move to voice-coil actuators from stepper-motor designs. Today, improvement is evolutionary, done by increasing the strength of the actuator itself, reducing the weight and size of the actuator arms and sliders, and tweaking other design parameters.

The characteristics of the actuator also have an impact, albeit relatively minor, on transfer performance. The reason is that the actuator has an impact on cylinder switch time, which is a component of sustained transfer rate. Again, the impact is relatively small compared to the impact of the other factors that influence STR.

Next: Spindle Motor Speed and Power

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