Platter Substrate Materials
The magnetic patterns that comprise your data are recorded in a very thin media layer on the surfaces of the hard disk's platters; the bulk of the material of the platter is called the substrate and does nothing but support the media layer. To be suitable, a substrate material must be rigid, easy to work with, lightweight, stable, magnetically inert, inexpensive and readily available. The most commonly used material for making platters has traditionally been an aluminum alloy, which meets all of these criteria.
Due to the way the platters spin with the read/write heads floating just above them, the platters must be extremely smooth and flat. With older, slower spindle drives and relatively high fly heights, the uniformity of the platter surface was less of an issue. Now, as technology advances, the gap between the heads and the platter is decreasing, and the speed that the platters spin at is increasing, creating more demands on the platter material itself. Uneven platter surfaces on hard disks running at faster speeds with heads closer to the surface are more apt to lead to head crashes. For this reason many drive makers began several years ago to look at alternatives to aluminum, such as glass, glass composites, and magnesium alloys.
Hard disk platters are very smooth, right? Well, not to a scanning electron microscope!
The image on the left is of the surface of an aluminum alloy platter; the one on the right
is a glass platter. The images speak for themselves. The scale is in microns..
Composed from two original images © IBM Corporation
Images used with permission.
http://www.pcguide.com/ref/hdd/op/mediaMaterials-c.html
The magnetic patterns that comprise your data are recorded in a very thin media layer on the surfaces of the hard disk's platters; the bulk of the material of the platter is called the substrate and does nothing but support the media layer. To be suitable, a substrate material must be rigid, easy to work with, lightweight, stable, magnetically inert, inexpensive and readily available. The most commonly used material for making platters has traditionally been an aluminum alloy, which meets all of these criteria.
Due to the way the platters spin with the read/write heads floating just above them, the platters must be extremely smooth and flat. With older, slower spindle drives and relatively high fly heights, the uniformity of the platter surface was less of an issue. Now, as technology advances, the gap between the heads and the platter is decreasing, and the speed that the platters spin at is increasing, creating more demands on the platter material itself. Uneven platter surfaces on hard disks running at faster speeds with heads closer to the surface are more apt to lead to head crashes. For this reason many drive makers began several years ago to look at alternatives to aluminum, such as glass, glass composites, and magnesium alloys.
Hard disk platters are very smooth, right? Well, not to a scanning electron microscope!
The image on the left is of the surface of an aluminum alloy platter; the one on the right
is a glass platter. The images speak for themselves. The scale is in microns..
Composed from two original images © IBM Corporation
Images used with permission.
http://www.pcguide.com/ref/hdd/op/mediaMaterials-c.html
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