Hard disk or solid-state? Think again

Though solid-state drives are in vogue, market forces and technical issues are giving the venerable hard-disk drive new life.

DRAMexchange, a Taipei-based market intelligence firm, said last week that the adoption of solid-state drives by computer vendors has slowed as the price of the NAND chips--the raw material of solid-state drives--has increased. The firm also said that computer makers have been cautious about using solid-state drives because current Windows operating systems are not fully optimized for SSDs.

Numonyx NAND flash chip

(Credit: Numonyx)

And the popularity of flash storage is waning in Netbooks. These tiny laptops at one time used solid-state drives almost exclusively. But Acer, Hewlett-Packard, Dell and others are moving en masse to configurations with large hard-disk drives in lieu of smaller-capacity solid-state drives.

SSDs typically offer higher performance--often much higher performance--than hard-disk drives and are more durable since they have no moving parts.

While those merits still apply, lingering doubts about the long-term retention of the data in a solid-state drive is making the hard disk look not quite so pass?. Ed Doller, the chief technical officer of Numonyx, a flash memory chip maker which was spun off from Intel and STMicroelectronics last year, addressed this issue in a recent phone interview. Numonyx makes two kinds of flash: NOR, used for storing computer programs, and NAND, used widely as a data storage medium in digital cameras, media players, smartphones, and solid-state drives.

"It's if versus when. With a hard drive it's if it's going to fail. With an SSD, it's when is it going to fail," Doller said, who critiques NAND only because his company is looking for a new storage medium--such as phase change memory--that can overcome some of NAND's inherent limitations.

Doller spoke about an epiphany he had after booting up a 20-year-old IBM AT. "I fired that thing up and it actually booted from the hard drive. If that same computer had been built with a solid-state drive, I can almost guarantee you that would not have worked. It would have lost its information over that period of time," Doller said.

Doller says NAND storage will get even more dicey as the densities increase--squeezing more memory cells into smaller areas. NAND is classified as a non-volatile memory device because it won't lose its data contents when the computer is turned off--just like a hard disk drive. Dynamic random access memory, or DRAM, used as the main memory in all PCs, does lose its contents when the computer is powered off.

"When you're talking about a non-volatile memory device, there's really only two things that matter. The first one being how many times can you write (data) to the device. And the second is how long will the data be in the device," he said. "Over time we've given up in the areas of those two very important parameters," he said.

Doller continued. "It's one thing to produce a 34-nanometer NAND device that's good enough for a card for your phone. It's another thing to say that I'm going to sell that same 34-nanometer to somebody who's going to build a solid-state drive for the (corporate) enterprise."

Controller chips, integrated into the flash memory device, can mitigate the shortcomings of flash-based storage by managing how the data is stored, Doller said. For example, moving stored data around the device--called "wear leveling"--to avoid using one area of the disk over and over again. For solid-state drive suppliers like Samsung and Intel, the controller chip is the secret sauce for not only managing how the data is stored but boosting performance.

The problem, according to Doller, is that the user must implicitly trust the designer and manufacturer of the drive. "Whoever is building that drive has to have very intricate knowledge of how you and your operating system are using that non-volatile memory," he said. If the SSD technology is not top-notch, disk failure can occur.

Phase change memory--the next phase?
What Numonyx's solution? Phase change memory. Last week, Samsung and Numonyx announced they are jointly developing market specifications for phase change memory (PCM) products. Phase change memory can read and write data very quickly at lower power than conventional NOR and NAND flash memory, and single bits can be changed to either 1 or 0 without the need to first erase an entire block of cells--a shortcoming of flash.

Phase change memory will also be "executable", allowing a separation of code and data for reliable code storage--particularly useful in handsets.

Sounds good, right? But phase change memory has one big problem. Chipmakers have been talking about phase change for decades. Companies typically develop a phase change prototype and tout its merits, then do not follow through.

Doller has a Trojan horse strategy.

"Put some PCM into that (solid-state) drive to make it easier for you to manage the media behind it. Once the PCM gets in there--maybe it's one percent, two percent of the overall memory--my belief is that it will act like a Trojan horse. Once it is in there customers will understand it improves reliability, it improves performance," he said.

This will increase demand, forcing manufacturers to ramp up production and, eventually, bring down costs in line with flash memory.