DRAM - What are memory module RANKS and how are they used ?

A RANK is a 64bit (or in a case of an ECC module 72bit) data width addressable area of a memory module.

Currently a module can be:
SINGLE RANKED (Rank 1  ) or
DOUBLE RANKED (Rank 2) or
QUAD RANKED (Rank 4 ).

1 RANK = 64bit width (or 72bit with ECC)

Single Rank  = 64bit

Double Rank = 64bit + 64 bit

Quad Rank  =  64bit + 64 bit + 64bit + 64 bit

Ranks are for interleaving to make a system run faster. This is where one device or part of a device is being accessed for data whilst another device or part of a device is getting ready to deliver data.

On some server upgrades there will be a maximum number of ranks a server will address or certain ranked modules may need to be fitted to certain sockets. For example, if a server can address 8 ranks. It may take a variation of 1GB, 2GB, 4GB and 16GB module to achieve this.

For 2GB modules the server may take:
4 x 2GB Rank 2 modules = 8 Ranks with 8GB or

8 X 2GB Rank 1 modules = 8 Ranks with 16GB

or alternatively using 16GB modules,
2 X 16GB Rank 4 modules = 8 Ranks with 32GB

Some planning is required when completing some server upgrades that need ranking, as installing the incorrect amount or type of ranks may lead to problems, or memory may need to be removed and replaced in the future to achieve the maximum density of memory if all sockets are used. Please check your user manual

Below are memory modules currently available from integral memory.

Technology DDR DDR2 DDR3
Density      
256MB RANK 1    
512MB RANK 1 or 2 RANK 1 or 2  
1GB RANK 1 or 2 RANK 1 or 2 RANK 1
2GB RANK 1 RANK 1 or 2 RANK 1 or 2
4GB   RANK 2 or 4 RANK 2 or 4
8GB   RANK 2 RANK 2 or 4
16GB     RANK 4

 

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