                                                                                
       IBM OEM STORAGE PRODUCTS:  A TECHNICAL BRIEF                             
                                                                                
                                                                                
                   GLASS SUBSTRATES                                             
                          IN                                                    
                 2.5" HARD DISK DRIVES                                          
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
 How is the media in disk drives constructed?                                   
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 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?                                         
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 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?                                                
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 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?                        
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 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.                                           
