







Samsung announced today that it has begun volume production of its 8Gb LPDDR4 memory chips, with expected commercial shipments in 2015. The announcement is noteworthy for a number of reasons. First, one of the most important characteristics of a modern mobile device is its battery life, and moving to a new memory standard should significantly reduce the memory subsystem's power consumption.Second, however, there's the clock speed. Samsung is claiming that its LPDDR4 will hit 3.2GHz, and while bus widths on mobile parts are significantly smaller than the 64-bit channels that desktops use, the higher clock speed per chip will help close that gap.In fact, multiple vendors have predicted that LPDDR4 clock speeds will actually outpace standard DDR4, with a higher amount of total bandwidth potentially delivered to tablets and smartphones than conventional PCs will see. Meanwhile, the power savings are expected to be substantial.This graph shows two important facets of DDR4 vs. DDR3 . The blue bar shows total bandwidth on the right -- LPDDR4-equipped devices should eventually hit 35GB/s, compared to 17GB/s for DDR3. Meanwhile, the total energy expended per bit of data read (in picojoules) drops sharply, from 4 pJ with LPDDR3 to less than 2 pJ for LPDDR4. That shift will pay dividends in mobile devices, though the actual improvement in any given family will depend on a number of additional factors. OEMs tend to set different memory clock speeds and bandwidth targets for different products -- an LPDDR4 device that emphasizes low power operation will still consume less power than the kinds of high-end devices shown above.The other thing to keep in mind is that while LPDDR4 clock speeds will rise more swiftly than on the desktop, desktop memory channels are twice the width of their mobile counterparts. That will work to balance the equation to some extent. Combine it with the fact that desktop memory will target lower latencies and more aggressive performance optimizations, and there's no serious risk of a desktop or laptop DDR4 system being outperformed by a tablet or smartphone in an apples-to-apples real-world comparison, regardless of what synthetic tests may imply.All of that said, however, weseeing mobile bandwidth rise sharply, driven in no small part by the rise of high-resolution mobile displays. If you want to drive 4K content to a smartphone or play a title in that mode (even a simple one), you need more bandwidth than LPDDR3 can provide. We've already seen Apple's A7 and A8 SoCs adopt larger on-die caches for precisely the same reason that conventional CPUs use them -- larger caches remove pressure from the memory bus and improve overall utilization.As of now, no manufacturers have announced plans to adopt LPDDR4 in specific products, but once Samsung is shipping in volume we'll undoubtedly see subsequent launches in short order. A debut in the inevitable Galaxy S6 wouldn't be at all surprising.