A Basic Understanding of Platter Sizes

The size of the platters is the key factor in determining the physical dimensions of hard drives. Since most drives are manufactured for use inside a PC they are produced in a few standard sizes. These standards are called hard disk form factors and primarily refer to the drives exterior dimensions. Often disks are referred to by their form factor; i.e. a 3.5 inch hard disk. As a general rule, the platter size of the disk is the same for all drives of a given form factor. This is not always true though, especially with the newest drives. But, every platter in any specific hard disk has the same diameter.

Today, undoubtedly the most common hard disk platter size in the PC world is 3.5".  Hard drives used in laptops are smaller due to consumers' boundless quest for "lighter and smaller". The platters on these drives are usually 2.5" in diameter or less; however, drives with 1.8" or even 1.0" platters are being seen more frequently in portable devices.

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Listed below are some of the key factors behind companies are moving toward smaller platters even for desktop units:

----Improved Rigidity: The rigidity of a platter refers to how inflexible it is. Rigid platters have added resistance to shock and vibration. They are a better match for being paired with higher-speed spindles and other high-performing hardware. Reducing the hard disk platter's diameter by a factor of two nearly quadruples its rigidity.

----Manufacturing Ease: The smoothness and evenness of a platter is essential to its quality; an ideal platter is absolutely flat and consistent. Flawed platters lead to a decreased manufacturing yield as well as possible data loss because of the heads coming in contact with uneven areas on the surface of a platter. Smaller platters are easier to make than larger ones.

----Decrease in Mass: Hard disk spindles are escalating in speed providing improved performance. Smaller platters are easier to spin, require less-powerful motors and they come up to speed quicker from a stopped position.

----Power Conservation and Noise/Heat Reduction: The use of power, especially for mobile computing, has always been an issue. Smaller drives commonly use a smaller amount of power compared to larger ones which in turn produces less noise and heat.

----Improved Seek Performance: Decreasing the size of the platters decreases the distance in which the head actuator must move the heads side-to-side performing random seeks thus improving seek time and making random reads/writes more efficient.