Configuring and using DDR3 memory with HP ProLiant Gen8 Servers

DDR3 DIMM types

ProLiant Gen8 servers support four different DIMM types – Unbuffered with ECC Memory (UDIMMs), Registered Memory

(RDIMMs), Load Reduced Memory (LRDIMMs), and HyperCloud Memory (HDIMMs). UDIMMs and RDIMMs are familiar from

their use in both ProLiant G6 and G7 servers. However, LRDIMMs are a new class of DIMMs that work solely with the

ProLiant Gen8 server architecture. HyperCloud DIMMs are special purpose memory available only as a Factory Installed

option. Each type of memory has its unique characteristics, and the type of memory you use may depend on the

application requirements for your server.

Unbuffered DIMMs

UDIMMs represent the most basic type of memory module. With UDIMMs, all address and control signals, as well as the

data lines, connect directly to the memory controller across the DIMM connector. UDIMMs offer the fastest memory

speeds, lowest latencies, and (relatively) low power consumption. However, they are limited in capacity. Unbuffered

DIMMs with ECC are identified with an E suffix in the manufacturer’s module name (example PC3L-10600E). UDIMMs are

applicable for systems needing the lowest memory latency at the lowest power at relatively low memory capacities.

Registered DIMMs

Registered DIMMs (RDIMMs) lessen direct electrical loading by having a register on the DIMM to buffer the Address and

Command signals between the DRAMs and the memory controller. This allows each memory channel to support up to

three dual-rank DIMMs in ProLiant Gen8 servers, increasing the amount of memory that a server can support. With

RDIMMs, the partial buffering slightly increases both power consumption and memory latency.

Load Reduced DIMMs

Load Reduced DIMMs are available for the first time with the ProLiant Gen8 servers. LRDIMMs use a memory buffer all

memory signals and to perform rank multiplication. The use of rank multiplication allows ProLiant Gen8 servers to

support three quad-ranked DIMMs on a memory channel for the first time. You can use LRDIMMs to configure systems

with the largest possible memory footprint. However, LRDIMMs use the most power and have the highest latencies for

the same memory clock speeds.

HyperCloud DIMMs

HyperCloud DIMMs (HDIMMs) are a new DIMM type designed to support 3 DIMMs per channel running at 1333 MT/s.

Because they use a different buffer architecture, HDIMMs will only operate at 3 DIMMs per channel and with all memory

channels populated. For HP ProLiant Gen8 servers, HDIMMs are only available as a Factory Installed Option and solely for

the Proliant 380p and the ProLaint 360p servers.

Comparing DIMM Types

Table 2 provides a quick comparison UDIMMs, RDIMMs, LRDIMMs and HDIMMs for ProLiant Gen8 servers using the 2P

Intel architecture.

Table 2. Comparison of UDIMMs, RDIMMS, LRDIMMs and HDIMMs for ProLiant Gen8 servers

Feature UDIMM RDIMM LRDIMM HDIMM

DIMM Sizes Available 2 GB, 4 GB, 8 GB 4 GB, 8 GB, 16 GB 32 GB 16 GB

Low power version of DIMMs available Yes Yes Yes Yes

Advanced ECC support Yes Yes Yes Yes

Address parity No Yes Yes Yes

Rank Sparing Yes Yes Yes Yes

Lock-Step Mode Yes Yes Yes Yes

Relative Cost Lower Higher Highest Higher

Maximum capacity on a server with 16

DIMM slots

128 GB 256 GB 512 GB N/A

Maximum capacity on a server with 24

DIMM slots

128 GB 384 GB 768 GB 384 GB only