Do you think 7mm-thick HDDs are a bit too fat? Western Digital claims it has a solution-- a hybrid HDD only 5mm-thick designed for integration in the thinnest of laptops.
Currently in sampling stage, WD gives few details on the slim HDDs other than "5mm hybrid HDDs will enable the market’s thinnest PCs to offer 500 GB of capacity, utilizing almost 50% less volume compared to current 9.5mm HDDs at 10% the cost of similar capacity SSDs." Interesting claim, that.
The drives pair MLC NAND flash storage with magnetic disks, with enterprise-style tiered storage placing "hot" (or more frequently used) data on NAND flash while "cold" (less accessed) data goes in the HDD.
Of course, WD is hardly the only storage vendor looking into even thinner HDDs-- Acer and Asus are working on similar projects for use in future Aspire and Zenbook ultrabooks.