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Phase Change Memory Points To Future of Storage
An anonymous reader writes
"A UC San Diego team is about to demonstrate a solid state storage device that it says provides performance thousands of times faster than a conventional hard drive and up to seven times faster than current state-of-the-art solid-state drives. The drive uses first-of-its-kind phase-change memory, which stores data in the crystal structure of a metal alloy called a chalcogenide. To store data, the PCM chips switch the alloy between a crystalline and amorphous state based on the application of heat through an electrical current. To read the data, the chips use a smaller current to determine which state the chalcogenide is in."
To store data, the PCM chips switch the alloy between a crystalline and amorphous state based on the application of heat through an electrical current.
That seems like probably not a very good idea, and I'm sure it will end up being one of the major hurdles to this technology really getting off the ground. What happens when the memory is heavily used (leading to buildups of heat in the memory that could cause unintentional bit changes)? Obviously the heat used to flip the bits must be dissipated very, very quickly, and that's a pretty challenging problem in its own right. Also, what happens to system temps when you use this memory? Many systems are already difficult to keep cooled, and adding another source of heat could be a particularly bad idea. Heck, what if the increase in system temps leads to memory faults? After looking over the Wiki, the last question seems unlikely to be a problem, but heating something to >600C seems like it could make it very hard to use this tech in heavy use situations.
So, what's up with the name of the system, "moneta", is it what I think it is (a Russian word for 'coin'), or is there something else at play here? I am a bit confused, because in the article, (which I am sorry to admit I read), it mentioned a bunch of names, but none that were Russian sounding.
You can't handle the truth.
It's bit-erasable. You can write a single word to PCRAM, without having to do the read-erase-rewrite cycle that Flash requires over a large cell. This means that you can just map a PCRAM device straight into RAM and use it as (slowish) memory. This is great for things like applications - the entire binary can be run from the mass storage device, it doesn't need copying into memory (execute in place). For a mobile device, you could conceivably have PCRAM as your main memory and 256MB or so of DDR as level-4 cache. When you're in standby mode, power down the DDR entirely, and your power usage drops to zero. Unlike suspending to disk or flash, you can resume instantly.
It's fast. Response times for PCRAM are somewhere around the 70ns mark, while flash is measured in ms. 70ns is about the speed of main memory a decade ago. This means that you can have non-volatile storage that's not much slower than RAM.
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It's not switching between solid and liquid. It's switching between crystaline and amorphous solid (stated in the first wikipedia intro, second link in the article). It takes a small amount of heat to make it switch between the two states, and they have different properties that can be measured, but both states are static in the absence of heat. What you described would make no sense at all, since if the PCB knows to provide heat to certain places then it already has external memory.
Of more interest is the security of the data stored in PCM. Can you erase it by putting it in a microwave? Leaving it in a hot car? Will it be easy to make a microwave beam/laser to erase parts of the drive from outside? The answer is probably no, but it will be very interesting to see the temperature specs on the resulting consumer products.