The power of persistent memory

Persistent memory could be the next big thing, says Tom Yager

I once reviewed a RAM-based storage device. It was a huge rack-mounted backplane equipped with memory cards and a SCSI interface. It was hot, loud and expensive, but I was convinced I had the future roaring away in my living room.

That was years ago, but the appealing concept of using memory as first-line storage stuck with me.

I’m a graduate of the “no moving parts” school of technology in many ways, so reliance on the magnetic orientation of metal particles as first-line storage strikes me as archaic.

Persistent storage started with the player piano roll, advanced to the wire recorder, and then it got stuck. The medium has changed, but like a wire recorder, a hard drive still flips the magnetic orientation of moving metal particles with an electromagnet.

Even as far as they’ve come, hard drives have been unable to unseat tape or flash memory in applications where you would expect they’d be the most useful.

Are you using hard drive cartridges for backup yet?

I talked with Apple about an oil exploration company that uses Xserve RAID to record seismic activity out at sea and then processes the data after the ship returns. The customer doesn’t pull the drive cartridges from the Xserve RAID chassis. It rolls the entire chassis, as a unit, off the ship. So would I, because I handle hard drives like eggs, and that’s not how I want to do business.

Wipe out all the tape and disk and give me memory instead. RAM is silent, it’s always online, and it very rarely grows defects. Even slow RAM runs rings around a fast hard drive, yet it is potentially more power-efficient because its power usage characteristics can be changed instantly during operation. In standby mode, which is sometimes called “suspend to memory”, RAM only draws the power needed to refresh the charge on memory cells.

My 17-inch PowerBook can hold 2GB of memory on standby power for close to a week. In contrast, the only thing you can do with a hard drive motor to make it draw less power is shut it off entirely.

I know memory’s not where it needs to be to push hard drives to the sidelines. Data written to the platters of well cared for hard drives lasts, while batteries eventually lose their juice and whatever RAM they were protecting fades away.

Flash memory isn’t nearly fast or dense enough to take over for disks in systems and its lifetime is limited, usually to a maximum of 100,000 write cycles. Even though that’s more than a tape can endure, it’s nothing compared to a hard drive.

On the far horizon, memory’s prospects as a first-line persistent storage medium are bright. Flash technology is evolving. Some current devices are able to sustain a million writes, and we should expect order-of-magnitude improvements to lifetime, density and performance.

For example, non-volatile RAM, which places a smaller battery close to each RAM chip or bank, is as fast as any other RAM but can hold its data for an estimated five years. That’s roughly the lifetime of a hard drive.

The future will undoubtedly take us to small, fast, multi-terabyte hard drives. Persistent memory storage, however, will proceed on a parallel track to provide options for high-end applications, gaining momentum as volume sends component costs down. Persistent memory technology will take time to make it to the larger market, but I’m ready for it now.

Yager is chief technologist at the InfoWorld Test Centre. Email him at

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