Greener computing, computers that use significantly less power, might be coming soon. How?
They turn themselves off between every keystroke, mouseclick, or touch.
The Journal of Applied Physics has published a very interesting article this week. The technology, Magneto-resistive Random Access Memory (MRAM), is over a decade old now. It uses two plates which can each be assigned a magnetic field direction. The data is read back by measuring the resistance across the plates, if the reading is low resistance then the fields are aligned. High resistance means they are opposing.
The size of the cells in in MRAM (each cell can store a bit) and the high current necessary to program them are the limiting factors in this technology, but enter the Spin Transfer Torque methodology. This concept uses the spin direction of electrons to modify the magnetic properties, drastically shrinking the cell size, which increases the memory density. This technology still has some development, but it has the advantage of significantly lower power demands.
Conventional DRAM requires a relatively high percentage of a computer’s power demands, it uses a small capacitor to store an electric charge with a transistor to control it. This means it is constantly drawing current from the main computer power source. MRAM-STT needs power when modifying a bit, but otherwise can be shut down. For any given bit in memory, it is likely that it spends more time being unchanged than changed, meaning the majority of time it can be shut down. The concept of the article is that it would be possible to build a computer that shuts itself down whenever there is a break in usage of a few milliseconds, then turn itself instantly back on. The power savings would be immense, and could allow computers to be run off alternative energy sources (solar, hand-crank, thermal).
There are quite a few details yet to be worked out. If you were to read through the journal article, you would see that there are still limitations in size and speed, but the analysis shows that we are still moving toward the end goal of a more energy efficient computer. Personally, I’m looking forward to cell phones that can last through the day while actually using them continuously.
K. Ando, S. Fujita, J. Ito, S. Yuasa, Y. Suzuki, Y. Nakatani, T. Miyazaki, and H. Yoda. Spin-transfer torque magnetoresistive random-access memory technologies for normally off computing. Journal of Applied Physics, 2014 DOI:10.1063/1.4869828