IBM OEM STORAGE PRODUCTS: A TECHNICAL BRIEF GLASS SUBSTRATES IN 2.5" HARD DISK DRIVES How is the media in disk drives constructed? -------------------------------------------- In today's environment, most disk drive platters are based on an aluminum substrate that is covered by a layer of chrome, a magnetic layer of both cobalt and chrome, a wear resistant carbon overcoat, and finally a layer of lubricant for improved wear. What is different in glass substrates? -------------------------------------- As the name suggests, the traditional aluminum substrate is replaced by a glass substrate. The magnetic layer, carbon, and lubricant layers stay the same. What are the benefits of glass? ------------------------------- For its weight, glass is much stronger than aluminum. Thinner and lighter disks can be used without compromising any of the properties needed for a robust platter. In fact, glass offers superior characteristics in the following areas: Hardness: When a drive is subjected to shock, as when dropped, the force can cause the recording head to come in contact with the disk and leave small indentations. The depth of indentation can make it impossible to read data which was previously recorded. Due to the superior hardness of glass, a glass substrate can withstand up to and beyond 500g's of non-operating shock, and 100g's of operating shock. Stiffness: Because glass is much more stiff than aluminum, the disk can be thinner. Because the glass is thinner, the platter weighs less. Lighter platters are easier to control if the file is dropped. The possibility of a disk slipping is reduced. Also, the weight of the platter is less likely to damage a spindle bearing. Are there any abnormal manufacturing issues with glass? ------------------------------------------------------- Because the magnetic layer is also conductive, the substrate does not negatively affect ESD. The chrome layer acts like a Leyden jar, and all charge is present on the outside of the disk. There is no difference in ESD precautions when handling glass. While glass does need special processing steps--special heat treatment and grinding on the edge to prevent chipping--glass does have very high yield rates, which allow it to be priced very competitively in the marketplace. Are there any other advantages to glass? ---------------------------------------- Because the disks are thinner, the gaps between the disks are larger than they would be if we had aluminum disks. This allows IBM to produce designs that stay well within clearly understood design criteria. We believe that this contributes to produce an extremely reliable drive. If glass is so great, why don't you use it on all your disks? ------------------------------------------------------------- Peripheral Research Corporation has projected that glass substrates will go from 1.8% of the market in 1994, to 37.7% of the market in 1997. So glass is an emerging technology. Due to the robustness of glass, IBM has implemented this technology first in those hard disks that are traditionally subjected to more shock and vibration. However, IBM will continue to examine the use of glass in all of our products.