SK Hynix has recently added single-die DDR4 memory chips featuring 16 Gb capacity to its product catalog. The benefit of the increase in single-die capacity is two fold: not only will the new components enable the company to build high-capacity memory modules using fewer chips, but also it will enable SK Hynix and its partners to build 256 GB DDR4 memory modules for ultra-high-end servers.

16 Gb DRAM chips per se are not exactly a breakthrough. Memory makers, including SK Hynix, already build high-capacity DRAM components by stacking two or four 8 Gb memory dies vertically using TSVs to get 16 Gb and 32 Gb components, then use such chips to build memory modules featuring 64 GB and 128 GB density. Stacking makes organization of DIMMs very complex: in the case of a 64 GB module we are dealing with a quad-ranked DIMM (featuring two physical and two logical ranks), whereas a 128 GB module is octal ranked (featuring two physical ranks and four logical ranks). LRDIMMs have a relatively high latency in general (because they use additional buffers), meanwhile complexity of 64 GB/128 GB LRDIMM architecture forces module makers to increase them even further (to CL20/CL22 for DDR4-2400/DDR4-2666 speed bins).

By contrast, SK Hynix has managed to develop single-die 16 Gb DDR4 components. Such ICs enable producers to build client memory modules or subsystems with a fewer number of chips, lowering power consumption, and allows server-class DIMMs with densities of up to 256 GB. When it comes to servers, the 16 Gb DDR4 components will allow to build dual-ranked 64 GB modules, quad-ranked 128 GB LRDIMMs and octal-ranked 256 GB LRDIMMs.

Do not expect the 256 GB modules to show up tomorrow, but the importance of ultra-high-density LRDIMMs is hard to overestimate. For example, if the microcode is adjusted to allow it, a single socket Xeon Scalable platform featuring an -M suffixed processors with 12 total memory slots could potentially support 3 TB of six-channel memory. Meanwhile, an AMD EPYC-based system can currently support 2 TB of eight-channel memory per CPU socket, and these modules could help support double that. For in-memory applications like huge databases, the more DRAM they can get the better. Undoubtedly, 128 GB and 256 GB memory modules will come at a price. For example, Crucial sells its 128 GB DDR4-LRDIMM for $3999.99 in retail, so a 2X capacity module would cost considerably higher.

SK Hynix’s 16 Gb DDR4 chips are organized as 1Gx16 and 2Gx8 and supplied in FBGA96 and FBGA78 packages, respectively. At present, 16 Gb memory components are rated to operate in DDR4-2133 CL15 and DDR4-2400 CL17 modes at 1.2 Volts. Sometimes in the third quarter SK Hynix plans to add DDR4-2666 CL19 to the lineup. SK Hynix does not disclose which manufacturing technology it uses to make its 16 Gb chips, but it is logical to expect that the company uses a fabrication process with minimal feature sizes and high yields to make large dies.

General Specifications of SK Hynix's 16 Gb Chips Part Number Transfer Rate Latency Org. Pkg. VDD Availability H5ANAG6NAMR-TFC 2133 MT/s 15-15-15 1Gx16 FBGA96 1.2 V Now H5ANAG6NAMR-UHC 2400 MT/s 17-17-17 H5ANAG6NCMR-UHC 2400 MT/s 17-17-17 Q3 2018 H5ANAG6NCMR-VKC 2666 MT/s 19-19-19 H5ANAG8NAMR-TFC 2133 MT/s 15-15-15 2Gx8 FBGA78 Now H5ANAG8NAMR-UHC 2400 MT/s 17-17-17 H5ANAG8NCMR-UHC 2400 MT/s 17-17-17 Q3 2018 H5ANAG8NCMR-VKC 2666 MT/s 19-19-19

Keep in mind that it will take quite a while for server makers to validate 16 Gb chips and 2Hi/4Hi stacks based on them, so do not expect 256 GB modules to hit today’s servers shortly from now. In the meantime, 16 Gb DDR4 chips will enable makers of SO-DIMMs to build single-sided 16 GB DDR4 SO-DIMM modules. This will also allow thin laptops (that do not use modules, but rely on commodity memory) to install 16 GB of DRAM using eight chips. For any user wondering why most 13-inch notebooks do not want to use 16 GB of DRAM in all but the high-end specification, these chips should enable a nicer ecosystem for higher memory capacity small notebooks.

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