 By the 1990s the dollar value of magnetic recording devices produced by companies located in California's "Silicon Valley" exceeded the dollar value of semiconductor devices produced there leading some to suggest that a more appropriate name for this area would be "Iron Oxide Valley," after the magnetic material coating the disks.All three remaining firms still have significant activities in Silicon Valley, but no HDD manufacturing.Western Digital still manufactures its read-write head wafers in Fremont CA.