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Everspin Launches Non-Volatile MRAM That's 500 Times Faster Than NAND
MrSeb writes "Alternative memory standards have been kicking around for decades as researchers have struggled to find the hypothetical holy grail — a non-volatile, low-latency, low-cost product that could scale from hard drives to conventional RAM. NAND flash has become the high-speed, non-volatile darling of the storage industry, but if you follow the evolution of the standard, you'll know that NAND is far from perfect. The total number of read/write cycles and data duration if the drive isn't kept powered are both significant problems as process shrinks continue scaling downward. Thus far, this holy grail remains elusive, but a practical MRAM (Magnetoresistive Random Access Memory) solution took a step towards fruition this week. Everspin has announced that it's shipping the first 64Mb ST-MRAM in a DDR3-compatible module. These modules transfer data at DDR3-1600 clock rates, but access latencies are much lower than flash RAM, promising an overall 500x performance increase over conventional NAND."
It's actually very durable. "In contrast, MRAM requires only slightly more power to write than read, and no change in the voltage, eliminating the need for a charge pump. This leads to much faster operation, lower power consumption, and an indefinitely long "lifetime"." (https://en.wikipedia.org/wiki/Magnetoresistive_random-access_memory)
5x more power than NAND
This seems confusing to me, because arguably it's going to use significantly less power than NAND. If I have something to write and it takes NAND 10s at 10w to write it, that's 100J of energy. MRAM would take .02s at 50w, that's 1J of energy. Unless I'm missing something? Seems like they could have quoted that to be both more accurate and show their product in a better light.
They claim shipping, so... yeah, a product. However, not a retail product, from the sound of it. Nobody makes a populate-your-own SSD or such.
More importantly perhaps, MRAM supposedly doesn't suffer from the page problem that NAND requires. Individual bits are accessible for reading and writing conveniently, unlike NAND, which requires writing by page. In addition, MRAM is supposedly much more robust than NAND, surviving many more write cycles. It hasn't existed long enough to know this for sure, but in theory, these two advantages means an SSD controller for an MRAM SSD could be vastly simpler than the ones required for NAND. No need for wear-leveling or page rewrite logic. This should both reduce the expense of SSDs and increase their real world performance and reliability.
However, while the article summary blathers about "from hard drives to main memory", this is not a competitor to modern DDR SDRAM. Assuming the quoted 500X faster than NAND is accurate, MRAM latency should be on the order of 100 nanoseconds for a random read. (NAND read latency is on the order of 50 microseconds.) DDR SDRAM random read latency is on the order of 22 nanoseconds.
Having said that, it is comparable with SDRAM from a decade ago, which probably translates directly to modern mobile devices. Low power suspend mode using MRAM instead of SDRAM could conceivably lower mobile device power consumption and improve battery life. If manufacturers get really silly, in theory a mobile device could be built that doesn't distinguish between its main memory and its mass storage. The two functions would be served by the same solid state circuitry. Obviously accommodating such a hardware design would give the kernel guys fits, but it could simplify things in the software a great deal, and incidentally net an interesting performance gain that's visible to users. Notably, the process of launching a program consists of nothing more than creating a stack and a heap for it somewhere--the program's code can stay right where it is. This also results in the somewhat bizarre (to modern ears) situation where suspend mode consists solely of persisting the CPU's state. Memory state is already persistent, always. As a final side effect, once scaled to SSD capacities, a device operating as described above effectively has an absolutely absurd amount of main memory, in theory, equivalent to the entire remaining capacity of the mass storage device.
MRAM has been around in labs for 20 years now, so the possibility of this being a real, viable, product-ready device is reasonably high. MRAM doesn't suffer from Fusion Power Syndrome.