Phase-change memory tested in prototype SSD

Flash-based SSDs may be all the rage these days, but there's always something better lingering just around the corner. Here it is: researchers at the University of California San Diego have created a prototype solid-state drive based on phase-change memory. For those unfamiliar with the new memory type, Technology Review explains:

Onyx was built using prototype phase-change chips made by Micron, a company working to commercialize the technology. The chips store data in a a type of glass, using small bursts of heat to switch sections of the material between two different states, or phases, that represent digital 1s and 0s. In one phase, the atoms of the glass are arranged in an ordered crystal lattice, in the other they have an amorphous, disorganized arrangement.

Unlike flash memory, which can only write in block- or page-sized chunks depending on whether cells are occupied or empty, phase-change memory can write as little as one bit at a time. Goodbye block-rewrite penalty, hello performance with small, high-volume writes. The 8GB Onyx phase-change prototype is reportedly 70-120% faster than an unnamed "80GB flash drive made for use in servers" with kilobyte-sized writes. However, the very same phase-change SSD is "much slower" than the server drive when writing larger chunks of data.

Obviously, phase-change memory isn't ready for prime time. There's certainly merit to the technology, though. Remember, too, that it took a little while for the sequential throughput of flash-based SSDs to catch up to their blistering random I/O rates. And then it took a while longer for prices to become reasonable. Before phase-change memory becomes cheap enough to supply an entire drive, it's expected to be used as a cache in hybrid SSDs made up primarily of traditional NAND.

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