Impact of lowered voltages in DDR4

Higher memory load reduces achievable bandwidth (memory loading).

Conversely, moving to higher frequencies at the same load also is hard (if you are already operating at the max speed possible).

Similarly, moving to lower voltages exacerbates the problem.

And achieving reasonable bandwidth becomes harder.

Moving from the current 1.5V (standard), 1.35V (low voltage) to the 1.2V for DDR4 will pose a challenge as well.

Impact of low voltage on performance

The impact of low voltage can be seen on the performance figures from IBM (Romley):

http://www.redbooks.ibm.com/abstracts/tips0850.html
IBM System x3650 M4
IBM Redbooks Product Guide

Table 5. Maximum memory speeds:
.
RDIMM – quad-rank (4-rank) – at 1.5V
– 1 DPC at 1066MHz
– 2 DPC at 800MHz
– 3 DPC not supported (because 4 ranks x 3 DPC = 12 ranks which exceeds the 8 ranks per memory rank limit of current systems)
.
RDIMM – quad-rank (4-rank) – at 1.35V
– 1 DPC at 800MHz
– 2 DPC at 800MHz
– 3 DPC not supported (because 4 ranks x 3 DPC = 12 ranks which exceeds the 8 ranks per memory rank limit of current systems)

And from Dell (Romley 12G servers):

http://www.dell.com/downloads/global/products/pedge/poweredge_12th_generation_server_memory.pdf
Memory for Dell PowerEdge 12 th
Generation Servers

Table 3 – PowerEdge memory speeds by type and loading (on pg. 10)

RDIMM – quad-rank (4-rank) – at 1.5V
– 1 DPC at 1066MHz
– 2 DPC at 800MHz
– 3 DPC not supported (because 4 ranks x 3 DPC = 12 ranks which exceeds the 8 ranks per memory rank limit of current systems)
.
RDIMM – quad-rank (4-rank) – at 1.35V
– 1 DPC at 800MHz
– 2 DPC at 800MHz
– 3 DPC not supported (because 4 ranks x 3 DPC = 12 ranks which exceeds the 8 ranks per memory rank limit of current systems)

Thus for DDR4, the move to lower voltage (1.2V) will complicate the already hard problem of moving to higher speeds (2.5GHz) for DDR4.

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3 Comments

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3 responses to “Impact of lowered voltages in DDR4

  1. Pingback: DDR4 borrows from LRDIMM use of load reduction | ddr3memory

  2. Pingback: JEDEC fiddles with DDR4 while LRDIMM burns | ddr3memory

  3. Pingback: Memory buying guide – including 1.35V memory for Romley | ddr3memory

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