DDR4 Memory Technology

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Technical white paper | DDR4 Memory Technology on HP Z Workstations
Memory Module capacity calculation
As mentioned previously, capacity is calculated using DRAM characteristics, specically technology, width, and the
total number of ranks. ECC must be considered in calculating the amount of DRAMs needed, but the ECC DRAM(s)
are only used to hold the ECC values and should not be counted as part of the actual data payload which denes the
DIMM capacity.
To calculate the capacity of a DIMM, the type of DRAMs used must be understood. The width of the DRAM should be
used to nd the number of DRAMs needed to make up the data bus. The capacity per rank can then be calculated by
multiplying the number of DRAMs by the size of the DRAM, and further divided by 8 to convert bits into bytes. The
total DIMM capacity is nally calculated by multiplying the rank capacity and the number of ranks on the DIMM.
Below are two examples:
• 8 GB unbuered, dual-rank, ECC DIMM
– Rank width = [9 DRAM] x [x8 width] = 72 bits
– Rank capacity = [8 payload DRAM] x [4 Gb technology] / [8 bits] = 4 GB
– DIMM capacity = [2 ranks] x [4 GB per rank] = 8 GB
• 64 GB registered, quad-rank, ECC DIMM
– Rank width = [18 DRAM] x [x4 width] = 72 bits
– Rank capacity = [16 payload DRAM] x [8 Gb technology] / 8 bits = 16 GB
– DIMM capacity = [4 ranks] x [16 GB per rank] = 64 GB
The max capacity available today, with 8 Gb based RDIMMs, is 64 Gigabyte (GB).
Label decoder
The following should be used to understand key attributes about the type of memory that is loaded in a system.
When looking at the DIMM label, you should see the following format:
gggGB pheRx PC4v-wwwwaa-mccdt-bb
• ggg = Module total capacity, in gigabytes
• phe = Number of package ranks of memory installed and number of logical ranks per package rank.
– p = # of package ranks installed
– h = DRAM package type
– e = Logical ranks per package rank
Current available DIMM type support table
Unbuered Non ECC
Unbuered ECC Registered LR DIMM
Single rank X
X X
Dual rank X
X X X
Quad rank X X
Octal rank X
16 bit width DRAMs (x16) X
8 bit width DRAMs (x8) X X
X
4 bit width DRAMs (x4)
X X
ECC data protection on data X
X X
Parity protection on
Command/Address
X X
X X
Buered Command/
Address/Clk
X X
Buered data
X
3DS Technology
X