HDDs with a thickness of 5mm have been around since 2013 but the new form factor failed to gain adoption due to fierce price competition in the 7" tablet segment and insufficient demand for ultrabooks.
The sources pointed out that consumers should be able to see ultra-slim HDDs in mobile devices between the end of 2014 and early 2015, competing against SSDs for the mobile device storage market.
Western Digital and Seagate unveiled their 5mm ultra-slim HDDs in 2013, but projects adopting the new storage devices have been postponed as vendors are having trouble rising ultrabook market penetration above the 10-15% range, the sources noted.