Single Head HDDs - test-drb@ccmp.vtda.org

12 Jan 2011

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...
  Except for a few very odd ones (e.g. hard drives which
record analagoue
 singals such as analogue video [1]) every hard disk I've worked on has
 used both sides of all platters for something. Maybe not user data
 storage (for excample, it may contain servo information only), but there
 will be a head on it. 
Because of the enormous pressure to reduce cost, single headed drives are very common. 
And have been for as long as I've been in the HDD industry.  For example, current
technology is 667 or 750 GB per platter with 1TB/platter due in next 12 months.  Yet there
is a demand for 250, 300 or 500 GB drives for ultra low cost drives.  Especially in the
consumer electronics market - for example, DVRs and security systems.

Taking out the cost of one head can save $2.50 to $5.00 of manufacturing cost.  That is a
big chunk of the $25 manufacturing cost typical of the very low end drives.

Servo data has been embedded in the data surface for many many years.  Most current drives
generate their own servo information.  Current drives even have a different tpi for the
servo versus the data track, even though they are on the same surface.

Billy Pettit