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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 | Positioning Plus Transfer Performance Specifications ]

Spindle Speed

The hard disk spindle is the shaft upon which the platters are mounted; it is driven by the spindle motor, one of the most important components in the hard disk. Obviously, the faster the motor turns, the faster the platters spin. The spindle speed of the hard disk is always given in RPM (revolutions per minute). Typical speeds of drives today range from 4,200 RPM to 15,000 RPM, with 5,400 to 10,000 RPM being most common on desktop machines. See this operational discussion of spindle speed for a table of the most common speeds employed today and in the past, and a list of different applications that use them.

Spindle speed has gone from being one of the least-discussed to one of the most-discussed hard disk specifications in only a few short years. The reason is the creation of increasingly fast spindles. For the first several years that hard disks were used in PCs, they all had the same spindle speed--3,600 RPM--so there was literally nothing to talk about in this regard! Over time, faster drives began to appear on the market, but slowly, and starting with high-end SCSI drives not used in most systems. Once the trend started, however, and the obvious advantages of higher spin speeds became apparent, the trend accelerated. Still, it is only since about 1998 that mainstream IDE/ATA drives have been readily available for the desktop in spindle speeds higher than 5,400 RPM. The most common speeds today are 5,400 and 7,200 RPM, and 10,000 RPM IDE/ATA drives are likely just around the corner (since they are now standard on SCSI with the SCSI high-end moving to 15,000 RPM!)

Today, spindle speed is the first thing you really should look for when assessing a drive; the speed of the spindle is the primary method by which drives are categorized into "classes". Almost any 7,200 RPM drive will be faster, and more expensive, than a 5,400 RPM drive of the same size and generation. The spindle speed directly correlates to the drive's rotational latency, affecting positioning performance, and also influences the drive's internal transfer rate. However, there is more to this: the difference in speed between different classes of drives is due not only to the speed of the spindle, but the fact that manufacturers tend to design these drives to be faster in other ways as well, knowing they are targeting a market more concerned with all facets of performance.

The spindle speed is of course influenced primarily by the spindle motor's speed and power. However, there are other issues involved in designing higher-RPM drives: you can't just slap a faster motor into an existing model! The size and number of platters is also an important design consideration, and the areal density of the drive also has an impact--faster drives sometimes require reductions in density compared to slower drives.

In fact, the overall quality of the entire hard disk becomes much more critical the faster you spin the platters. Issues with higher-speed drives include increased noise and vibration, and cooling concerns, though these have improved greatly with second, third and subsequent generation high-speed drives.

Next: Areal Density

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