Help Me Choose - Memory

Help Me Choose - Memory

Dell EMC PowerEdge offers a variety of memory options to meet your workloads requirements. Memory plays a key role in your overall performance along with your processor, accelerator and storage choices.

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Properly configuring a server with balanced memory is critical to ensure memory bandwidth is maximized and latency is minimized. When server memory is configured incorrectly, unwanted variables are introduced into the memory controllers’ algorithm, which inadvertently slows down overall system performance. To mitigate this risk of reducing or even bottlenecking system performance, it is important to understand what constitutes balanced, near balanced and unbalanced memory configurations.

Variables such as DIMM consistency and slot population will dictate whether a configuration is balanced or unbalanced. Follow these guidelines at the socket and server level, to achieve a balanced memory configuration:

  1. 1

    Use 6 or 12 DIMMS per 2nd Generation Intel® Xeon® Scalable CPU for a balanced configuration.
    Use 8 or 16 DIMMs per 2nd Generation AMD EPYC™ CPU for a balanced configuration.
    Use 8 or 16 DIMMS per 3rd Generation Intel Xeon Scalable CPU for a balanced configuration.

  2. 2

    Use identical DIMMs (same capacity, rank and DIMM type)

  3. 3

    Use the same memory configurations for every CPU in the server.

  4. Intel® Optane™ Persistent Memory delivers a unique combination of an affordable large-capacity memory tier, with data persistence. Ideal for virtualization, databases and other demanding workloads.

  5. For situations that demand mixing DIMM sizes, all memory should be chosen based on identical rank structure, and all memory channels should be populated with an identical mix of DIMM types (ie RDIMMs cannot be mixed with LRDIMMs).

  6. Choose the appropriate processor to support the expected memory frequency.

Which DIMM Do I Need?

A DIMM — or dual in-line memory module — is a series of random access memory chips mounted on a small circuit board. DIMMs are installed in sockets on your computer's motherboard.

DIMM Types


Registered DIMM
Provides for higher capacity options and advanced RAS features. It is the most commonly used DIMM type, and offers the best mix of frequency, capacity, and rank structure choices


Load Reduced DIMM
Provides maximum capacity beyond that of an RDIMM but at a higher power consumption. Uses a buffer to reduce memory loading to a single load on all DDR signals, allowing for greater capacity.


Unregistered or Unbuffered DIMM
Provides low latency and low density. Used on single socket servers in the PowerEdge portfolio.


Intel® Optane™ Persistent Memory
Provides a large memory capacity at an affordable price. Any application can take advantage of DCPMM in Memory Mode with a compatible operating system. Unlock more performance as well as persistency when using an application that supports App Direct Mode. DCPMM is used in conjunction with RDIMMs or LRDIMMs and a maximum number of 6 DCPMMs can be used per CPU.


Non-Volatile DIMM
Provides a persistent memory solution with NAND and DRAM that maintains data in power loss, system crash, or normal shutdown. This solution requires a battery as a power source for an AC loss condition. It can be used in conjunction with RDIMMs.

Intel® Optane™ Persistent Memory (DCPMM)

Dell EMC PowerEdge integrates the Intel® Optane™ Persistent Memory Module to bridge functionality between traditional memory and storage. The advancement of memory capability is critical to accommodate growing customer needs. Data center utilization is not possible if memory bandwidth or capacity is bottlenecking system performance. Dell EMC PowerEdge servers configured with Intel® Optane™ Persistent Memory Modules focus on enabling the future of data center technology. Latency reduction is achieved by enabling core application data to be stored as non-volatile information; providing bandwidth support for large in-memory databases such as Microsoft SQL Server 2019. Furthermore, the substantial increase in memory capacity provides more resources to be used in large storage capacity environments such as VM scaling.

Intel® Optane™ Persistent Memory is a unique technology that bridges a gap between ‘memory’ and ‘storage’. Like RAM it sits within the PC memory hierarchy. By placing commonly used data and programs closer to the processor, Intel® Optane™ Persistent Memory allows the systems to access this information more quickly and improve overall system responsiveness. Intel® Optane™ Persistent Memory is designed to work in conjunction with DRAM not replace DRAM. These two memory technologies complement each other within the system. If all DIMM slots are being used, 50% of the DIMM slots will have DRAM and 50% of the DIMM slots will have Intel® Optane™ Persistent Memory.

Because of Memory Mode, Intel® Optane™ Persistent Memory can be used with almost any workload. In memory mode, the DRAM is used as a cache layer and the Intel® Optane™ Persistent Memory appears as the system memory. Any application can be used with a supported operating system. This allows a server to have a large memory footprint at a very compelling cost point. Because any application can be used, virtualization is a great use case for memory mode. Intel® Optane™ Persistent Memory is not persistent in Memory Mode.

App Direct Mode or Application Direct Mode is when an application can natively use Intel® Optane™ Persistent Memory which enables higher capacity (both the DRAM and Intel® Optane™ Persistent Memory are available to the system), can unlock higher performance, and that data stored on Intel® Optane™ Persistent Memory is now persistent. In order to use this mode, the application must state that it supports App Direct Mode. The application will know what data should be stored on regular DRAM and what data should be stored on Intel® Optane™ Persistent Memory. The software ecosystem and applications for App Direct Mode are growing every day and it is ideal for databases. In-memory databases can get to a very large capacity at a very compelling cost. Regular databases can increase performance by holding the entire database in Intel® Optane™ Persistent Memory instead of using SSDs and NVMe drives.

An operating system can use Storage over App Direct Mode to allow the Intel® Optane™ Persistent Memory to appear as a standard storage block device. Any application that can use storage block devices can use this mode without having to support App Direct Mode directly. Storage over App Direct Mode is great when you want to write data to a persistent fast device.

Frequently Asked Questions

DRAM stands for “dynamic random-access memory” and is the type of memory we use in servers. DDR4 stands for “double data rate type four” and it is the generation of memory that is currently used in servers.

If a balanced configuration of sixteen or eight DIMMs per CPU cannot be implemented, then the next best option is a near balanced configuration.To obtain a near balanced population, populate four or twelve DIMMs per CPU in sequential order. When any number of DIMMs other than 4, 8, 12 or 16 is populated, disjointed memory regions are created making NPS 4 the only supported BIOS option to select. Click here to learn more.