27-09-2012, 05:01 PM
Slashing Energy Needs for Next-Generation Memory
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ABSTRACT
A new data-encoding scheme this week that slashes more than 30 percent of the energy needed to write data onto new memory cards that use "phase-change memory" (PCM) -- a competitor to flash memory that has big backing from industry heavyweights.
PCM uses the same type of materials as those used in rewritable CDs and DVDs, and it does the same job as flash memory -- the mainstay technology in USB thumb drives and memory cards for cameras and other devices. IBM and Samsung have each demonstrated PCM breakthroughs in recent months, and PCM is ultimately expected to be faster, cheaper and more energy-efficient than flash.
"We developed an optimization framework that exploits asymmetries in PCM read/write to minimize the number of bit transitions, which in turns yields energy and endurance efficiency," said researcher Azalia Mirhoseini, a Rice graduate student in electrical and computer engineering, who presented the research results at DAC.
In PCM technology, heat-sensitive materials are used to store data as ones and zeros by changing the material resistance. The electronic properties of the material change from low resistance to high resistance when heat is applied to alter the arrangement of atoms from a conducting, crystalline structure to a nonconducting, glassy structure. Writing data on PCM takes a fraction of the time required to write on flash memory, and the process is reversible but asymmetric; creating one state requires a short burst of intense heat, and reversing that state requires more time and less heat.
The new encoding method is the first to take advantage of these asymmetric physical properties. One key to the encoding scheme is reading the existing data before new data is written. Using a combination of programming approaches, the researchers created an encoder that can scan the "words" -- short sections of bits on the card -- and overwrite only the parts of the words that need to be overwritten.