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The Value of Using Four-Channel Optimized

AMD EPYC

CPUs in PowerEdge Servers

Introduction

Most 2

generation AMD EPYC

CPUs contain four memory controllers

each with two memory channels; a total of eight memory slots that need

to be populated for an optimized configuration. However, several CPU

SKUs were modified to optimize performance with only four memory slots

populated. These four-channel optimized SKUs require only two memory

controllers to be fully populated for an optimized solution, and ultimately

provide a lower cost alternative to traditional eight-channel solutions. The

remaining channels can always be filled in if more memory is required.

Four-Channel Architecture and Positioning

These four-channel optimized CPUs, such as the AMD EPYC

7252 and

the AMD EPYC

7282, contain a unique architecture that was designed

to best support two fully populated memory controllers. Figure 1 below

illustrates at a high level the architecture differentiation between four-

channel optimized and eight-channel optimized CPUs.

The Core Complex Die, or CCD, count is reduced from four to two per

CPU. Both memory controllers closest to the CCD quadrant should be

populated with two memory modules so the I/O die can route and distribute

data packages across the smallest travel distance possible. Populating

this way enables performance similar to eight-channel data transfer

speeds for specific workloads. Additionally, reducing the number of CCDs

lowers the total solution cost, effectively generating an increased

performance per price value proposition.

Tech Note by

Matt Ogle

Mohan Rokkam

Summary

AMD recently launched

their 2

generation of AMD

EPYC

CPUs, and with

this launch came the

announcement of an

additional set of four-

channel optimized SKUs.

Considering AMD CPUs

have eight memory

channels, there has been

uncertainty as to why these

SKUs were created and

how they are beneficial.

This DfD will educate

readers on the architecture

modifications made for

four-channel optimized

AMD EPYC

CPUs, as

well as the suggested use

cases and value they bring

to PowerEdge servers.

Figure 1 – Block diagram illustrating the distinctions between four-channel

optimized and eight-channel optimized architectures

Summary of content (2 pages)

PAGE 1
Server and Infrastructure Engineering Direct from Development The Value of Using Four-Channel Optimized AMD EPYCTM CPUs in PowerEdge Servers Introduction Tech Note by Matt Ogle Mohan Rokkam Summary AMD recently launched their 2nd generation of AMD EPYCTM CPUs, and with this launch came the announcement of an additional set of fourchannel optimized SKUs. Considering AMD CPUs have eight memory channels, there has been uncertainty as to why these SKUs were created and how they are beneficial.
PAGE 2
Copyright © 2020 Dell Inc. or its subsidiaries. All Rights Reserved. Dell, EMC and other trademarks are trademarks of Dell Inc. or its subsidiaries Positioning Various workloads were tested to compare performance with the eight-channel optimized SKUs. Most workloads do indeed gain an increased performance per price. Customers that prioritize pricing over everything else should find the cost-savings of four-channel optimized CPUs an attractive feature to consider.