[Moderator note: "Mass Storage: Flash, Magnetic, or Both?", which Joel Weiss discusses in the following writeup, will be the subject of my September 27, 2007 feature article in EDN. Joel and I both welcome your comments on his perspective of this controversial topic.]

Every day seems to bring a new prediction that hard drives will soon go the way of the floppy disk, due to the emergence of solid state drives. I understand the appeal of a good story as much as anyone. But what is the real story with hard drives versus solid state drives? Quite frankly, when you look beyond the hype, it’s clear that hard drives are (and will continue to be) the dominant storage choice.

At IDEMA, we see hard drives and solid state storage as complimentary and cooperative rather than competitive. We believe that the two can co-exist in harmony. Here's why:

• The cost and capacity of hard drives are unsurpassed, and this advantage is likely to continue in the years to come. Companies are shipping terabyte drives today, providing enormous amounts of storage for around $0.40 per gigabyte, while lower-capacity 400-500 GB drives are selling at on-line retailers for as little as $0.20 per GB. Solid state drives are increasing capacity while reducing cost, but even if this trend continues at the same rate in the future, it will not significantly close the gap that exists with HDD cost and capacity for many years.
• Hard drives have over 50 years of proven reliability. The high reliability requirements that have been a constant in the HDD industry require very accurate writes that are verifiable. Error rates are on the order of 1 bit per 1000 billion reads. This makes HDDs the preferred storage method for applications where data integrity is not an option, such as the IRS, the defense industry, the DMV, health care, banking, and many others. Before a new drive is shipped to a user, it has undergone stringent internal testing. Typically 50,000 to 200,000 drives are tested internally to ensure reliable operation prior to being released into production and shipped to customers. Conversely, flash drives have to date not had to meet this extremely high reliability rate. An error in your flash drive, which might cause you to miss a bit or pixel in a music or video application, is no big deal. However, if you have stored data-critical applications on flash storage, then it becomes a very big deal.
• Durability of hard drives has been under-estimated, under-estimating new technology that helps protect the drive. "Free-fall" sensors which can detect that a drive is about to "hit the floor", for example, protect the drive by moving the head to a safe place off the surface of the disk. If you drop your mobile computer, it’s much more likely you will break the LCD display than the hard drive. Sometimes I hear "flash-only" proponents claim that a flash drive can go through the washing machine and still work. Well, I know one man who (accidentally) put his hard drive through both the wash and dry cycle. Guess what? It still worked when he removed it from the dryer. Hard drives are successfully meeting the challenge of more extreme environments and increased shock and vibration demands. As hard drives become standard features in cars, HDDs are built to withstand the heat of an Arizona summer and the frigid cold of an Alaska winter.
• Technology challenges do exist for both hard drives and solid state drives. The hard drive is no stranger to technology transitions that have enabled it to continue its torrid pace of storage capacity increases in its 50-plus year history. A recent example was the transition to perpendicular recording. New technologies, such as "bit-patterned media" and "heat-assisted magnetic recording" will enable further capacity increases and reliability and durability improvements. The HDD industry has a strong track record when it comes to innovating and implementing new technologies. Technology challenges for solid state drives include narrowing line widths and transitioning to new solid-state storage technologies such as "phase-change". All of these aforementioned technology transitions require substantial investment in technology development and manufacturing scale-up.

Storage is a huge business: the overall storage market is forecasted to be $92 billion in 2007. Of this total, hard drives are projected to be $31 billion, NAND storage to be $34 billion, and NOR to be $8 billion (source: Gartner Forecast February 2007). We believe the real story is that there is not only room for both hard drives and solid state drives in this dynamic industry but new applications will demand even more innovation in the expanding world of content storage.