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DRAM Modules FAQs

DRAM Modules(3)
Can Vtt and Vref be supplied by the same supply in my system design?
With proper decoupling this can be an acceptable design. However, Micron recommends ensuring all supplies are separated. Vref tends to have more noise on it because it supplies signals that are regularly switching. A robust design would typically not connect these supplies due to the possibility of introducing this noise onto the Vtt plane which should be as stable as possible. Additionally, Vref requires much less current than Vtt.
Is there a set of trace lengths and routing rules that are standard for use when designing a system that uses a specific module technology and form factor?
No. A robust memory subsystem design that includes the use of 1 or more memory modules must be simulated in order to determine the optimum trace lengths, terminations. However, our design guides such as TN-47-01 and TN-41-08 have some best practices and design examples based on some typical system assumptions. This information is not meant to be the only way your system can be designed. It is a starting point and moreover an example of the steps used to determine the best design for your system.
NVDIMM(8)
What is NVDIMM?

NVDIMM is a nonvolatile persistent memory solution that combines NAND flash, DRAM and an optional power source into a single memory subsystem. Micron’s NVDIMM is capable of delivering the performance levels of DRAM combined with the persistent reliability of NAND, ensuring data stored in-memory is protected against power loss.

How do NVDIMMs work?

NVDIMMs operate in the DRAM memory slots of servers to execute workloads at DRAM speeds. In the event of a power fail or system crash, an onboard controller safely transfers data stored in DRAM to the onboard nonvolatile memory, thereby preserving the data that would otherwise be lost. When the system stability is restored, the controller transfers the data from the NAND back to the DRAM, allowing the application to efficiently pick up where it left off.

What is persistent memory?

Persistent memory is a new addition to the memory/storage hierarchy that enables greater flexibility in data management by providing nonvolatile, low-latency memory closer to the processor. Essentially, persistent memory accelerates application performance by removing what otherwise are constricting I/O bottlenecks placed on the application by standard storage technologies. By placing nonvolatile memory on the DRAM bus, this architecture enables customers to significantly optimize data movement in order to deliver faster access to variables stored in DRAM.

With persistent memory, system architects are no longer forced to sacrifice latency and bandwidth when accessing critical data that must be preserved. Critical data can be stored close to the processor, dramatically cutting access times. Persistent memory delivers a unique balance of latency, bandwidth, capacity and cost, delivering ultra-fast DRAM-like access to critical data and enabling system designers to better manage overall costs.

What are the key use cases for NVDIMM?

Any application where performance depends on variables stored in nonvolatile media (HDD or SSD) can benefit from NVDIMMs (most applications can be accelerated). Persistent variables include metadata logs, checkpoint state, host write caches, write buffers, journals and general logs. Applications that can be accelerated by placing these variables in NVDIMM include 2-node, high-availability storage using RAID cards, SSD mapping, RAMDisk and write caching for SSDs.

What products are available today?

Micron will be offering three DDR4 NVDIMM products:

  1. 8GB DDR4 NVDIMM with legacy firmware
  2. 8GB DDR4 NVDIMM with JEDEC firmware
  3. PowerGEM® ultracapacitor for 8GB NVDIMM
What is the difference between the legacy and JEDEC firmware?

Legacy firmware refers to the firmware features and controller register locations for features determined by AgigA Tech, Inc., for initial DDR4 NVDIMM designs. JEDEC has now standardized the NVDIMM firmware features, register locations and APIs so that one vendor’s NVDIMM can be compatible with any other vendor’s NVDIMM. All new Micron NVDIMM solutions will leverage the JEDEC firmware interface.

How will NVDIMMs be enabled? What platforms support NVDIMM?

Many motherboards, servers and storage appliances support NVDIMMs today. Many more will come to market in 2016. Contact your supplier for more details.

Are there software requirements for NVDIMM?

NVDIMMs leverage either block mode or direct access drivers. NVDIMMs used in conjunction with a block mode driver are compatible with OS and applications with little to no necessary software modifications. Additional performance capability can be tapped by leveraging an NVDIMM with a direct mapped driver, but OS and application software will likely need some modification. Micron is currently working with major OEMs and software companies to incorporate NVDIMM hardware, driver and software support into their mainstream products.