Single-, Dual-, And Quad-Rank Dimms; Memory Subsystem Architecture; Memory Protection Modes - HP ProLiant DL160 Gen8 User Manual

Item Description
For the latest supported memory information, see the QuickSpecs on the HP website
(http://h18000.www1.hp.com/products/quickspecs/ProductBulletin.html). At the website, choose the
geographic region, and then locate the product by name or product category.

Single-, dual-, and quad-rank DIMMs

To understand and configure memory protection modes properly, an understanding of single-, dual-, and
quad-rank DIMMs is helpful. Some DIMM configuration requirements are based on these classifications.
A single-rank DIMM has one set of memory chips that is accessed while writing to or reading from the
memory. A dual-rank DIMM is similar to having two single-rank DIMMs on the same module, with only one
rank accessible at a time. A quad-rank DIMM is, effectively, two dual-rank DIMMs on the same module. Only
one rank is accessible at a time. The server memory control subsystem selects the proper rank within the
DIMM when writing to or reading from the DIMM.
Dual- and quad-rank DIMMs provide the greatest capacity with the existing memory technology. For
example, if current DRAM technology supports 8-GB single-rank DIMMs, a dual-rank DIMM would be 16
GB, and a quad-rank DIMM would be 32 GB.
LRDIMMs are labeled as quad-rank DIMMs; however, they function more like dual-rank DIMMs. There are
four ranks of DRAM on the DIMM, but the LRDIMM buffer creates an abstraction that allows the DIMM to
appear as a dual-rank DIMM to the system. The LRDIMM buffer also isolates the electrical loading of the
DRAM from the system to allow for faster operation. These two changes allow the system to support up to
three LRDIMMs per memory channel, providing for up to 50% greater memory capacity and higher memory
operating speed compared to quad-rank RDIMMs.

Memory subsystem architecture

The memory subsystem in this server is divided into channels. Each processor supports four channels, and
each channel supports three DIMM slots.
For the location of the slot numbers, see "DIMM slot locations
This multi-channel architecture provides enhanced performance in Advanced ECC mode. This architecture
also enables Lockstep and Online Spare Memory modes.
DIMM slots in this server are identified by number and by letter. Letters identify the population order. Slot
numbers indicate the DIMM slot ID for spare replacement.

Memory protection modes

To optimize server availability, the server supports the following AMP modes:
•
Advanced ECC—Provides up to 4-bit error correction and enhanced performance over Lockstep
memory mode. This mode is the default option for the server.
•
Online Spare Memory—Provides protection against failing or degraded DIMMs. Certain memory is
reserved as spare, and automatic failover to spare memory occurs when the system detects a DIMM that
is degrading. This enables DIMMs that have a higher probability of receiving an uncorrectable memory
error (which results in system downtime) to be removed from operation.
Definition
E = UDIMM (unbuffered with ECC)
L = LRDIMM (load reduced)
("DIMM slots" on page 10)."
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