Micron is first to market with phase-change memory (PCM)By Rick Burgess
We've been hearing about phase-change memory (PCM) for the past several years, but it appears Micron will be the first manufacturer to bring this flash-alternative to commercial markets. According to Micron, PCM will be landing on feature phones first with plans for smartphones and tablets to come later.
If you're wondering why feature phones, Micron says it'll be stamping out boards with 1GB of PCM (45nm) accompanied by 512MB of LPDDR2 (mobile DDR). Smartphone and tablet users expect higher capacities, but PCM is very much in its infancy. Micron is likely taking a slow and steady approach before working with higher densities and smaller packages.
PCM is a type of non-volatile memory which appears to be best suited for applications where NAND flash is currently used. NAND flash is typically found in USB storage drives, SSDs, memory cards and most other commercial products where permanent data storage without a power source is important. PCM does this too.
What makes PCM different though is how it stores data. PCM works by triggering (pdf) a poly-crystalline solid to become amorphous, switching from its once crystalline state. This change is induced by applying jolts of electricity to specific areas of the material, creating heat and triggering those state changes. This type of localized "current injection" can be done with great precision, allowing PCM to manipulate individual "cells" as single bits, similar to SLC flash memory.
Unlike NAND flash though, PCM is bit-alterable. That means there's no need for PCM controllers to erase bits between re-writes. This is one reason current flash offerings have write speeds far below their read performance.
One more interesting bit – if PCM becomes fast enough, we may see the marriage of storage and system memory. In fact, Micron mentions this in this brief PCM demo.
Because system memory has needed to be both fast and affordable, the industry has been using volatile memory solutions like EDO, SDR and DDR for decades. Respective to their own time periods, these DRAMs offer great speed, but instantaneously lose any information they contain when the host device is powered off. Thus, for reasons of price and volatility, storage devices and system memory have remained two very separate things.
Like flash, PCM doesn't suffer from this memory loss. Unlike flash though, PCM and competing non-volatile technologies have the potential to rival the performance of DRAM. If these non-volatile memory technologies become fast enough, cheap enough and large enough – quite a few variables, I know – there may be little reason to keep memory and storage devices separate.