HyperCloud DIMMs

There is a fourth option: Netlist's HCDIMM. Netlist, a company that specializes in making VLP (Very Low Profile) memory, offers an alternative for LRDIMMs: HyperCloud DIMMs.


Instead of using a centralized buffer (LRDIMMs), HCDIMMs use a distributed buffer to reduce the electrical load on the memory channels. Combined with an HCDIMM register, four ranks are presented as two.

HCDIMM advantages
The advantage of HCDIMMs is that HCDIMMs run one speed bump faster than LRDIMMs. So while LRDIMMs have to throttle back to 1066MHz at 3 DPC, HCDIMMs run at 1333MHz. According to a Netlist sponsored report, HCDIMMs offer about 17% higher bandwidth, which sounds reasonable to us. Secondly, the distributed buffer architecture is the same architecture that DDR4 is converging on. However DDR4 will be running at a much lower 1.2V.

HCDIMM Disadvantages
The combination of a register and distributed buffers (and clock redundancy) comes with a serious drawback: power. Although we could not test HCDIMMs ourselves, most industry sources talk about 20% higher power than LRDIMMs, while LRDIMMs only consume more than RDIMMs with 1 DPC. In 3 DPC configurations, LRDIMMS consume about the same as RDIMMs.

Secondly, HCDIMMs are not a JEDEC standard. As a result the HCDIMM ecosystem—module, server and CPU vendors—is smaller. AMD and Intel do not officially validate HCDIMMs, so server vendors have do the complete validation effort themselves. IBM for example only offers them in one system (IBM system x3650 M4), and 16GB HCDIMMs are quite a bit more expensive than both 16GB LRDIMMs and RDIMMs. LRDIMMs are much more widespread; almost every server vendors supports them in a wide range of server models.

Lastly, HCDIMMs are only available from one module vendor, Netlist.

Nevertheless, HCDIMMs are viable but somewhat expensive alternative in the high capacity memory market if your server supports them. Netlist has been quite successful in convincing the server vendors: several models of HP, Supermicro, and Gigabyte support HCDIMMs. HP offers HCDIMMs in their most popular servers (DL380/DL360), although HCDIMMs can only be installed by HP.

Once Netlist gets the 32GB parts out in large volumes, the extra competition can probably drive prices down. Until then, HCDIMMs offer only a speed advantage over RDIMMs.


Let us structure all this info in a table.

DIMM Types, Speed, and Capacity Limitations
Maximum speed at 2 DPC 1333MHz 1600MHz 1333MHz 1333MHz 1600MHz
Maximum speed at 3 DPC Not possible 1333MHz 1333MHz 1066MHz 1333MHz
Maximum capacity per CPU (Quad channel) 64GB 192GB (3 DPC)
256GB (2 DPC)*
192GB (3 DPC)
256GB (2 DPC)*
384GB 192GB
Top speed at maximum capacity 1066 1066 (DR) **
800 (QR) **
1066 (DR) **
800 (QR) **
1066 1333
Voltage 1.5V 1.5V 1.35 V 1.35V/1.5V 1.35V/1.5V
loaded, 3 DPC Power usage (at 1.5V) per DIMM 4 W 4.5 W <= 4 W 5-6 W 8-9 W
Intel CPU support Xeon 5500
Xeon 5600
Xeon E5
Xeon 5500
Xeon 5600
Xeon E5
Xeon 5600
Xeon E5
Xeon E7
Xeon 5600
Xeon E5
Xeon E7
AMD CPU support Opteron 4000
Opteron 6100
Opteron 6200
Opteron 4000
Opteron 6100
Opteron 6200
Opteron 6100
Opteron 6200
Opteron 6200 N/A
Server support all servers all servers all servers Dell, HP, IBM,Supermicro HP DL360G8 DL380G8
IBM x3650 M4

* Quad Rank DIMMs require special BIOS support and validation and are not available on all servers.
** DR = Dual Rank, QR = Quad Rank.

1600MHz LRDIMMs are possible but not commercially available as far as we know. 32GB HCDIMMs are available in very small quantities. LRDIMMs are available from almost every server module manufacturer out there, while HCDIMMs are netlist modules only.


An Overview of Server DIMM types Benchmarking Configuration


View All Comments

  • ddr3memory - Monday, August 6, 2012 - link

    Your article is very interesting - and the first mainstream (and belated) examination of the LRDIMM (new standard - incompatible with RDIMMs) vs. HCDIMM (100% DDR3 RDIMM compatbile) choice for Romley.

    I have whittled down the use case for HCDIMMs/LRDIMMs and RDIMMs as follows:

    The HCDIMM use case is at:
    - 16GB at 3 DPC use
    - 32GB (outperform both RDIMMs and LRDIMMs)

    LRDIMMs are not viable at:
    - 16GB (RDIMMs are better)
    - 32GB (HCDIMMs are better)

    RDIMMs are not viable at:
    - 32GB (because they are 4-rank - trumped by LRDIMMs/HCDIMMs)

    There is a reason the Netlist HCDIMMs were only released on the virtualization servers from IBM/HP - because at 16GB levels the only niche available for LRDIMM/HCDIMM vs. RDIMM is the 3 DPC space. This will expand considerably at 32GB to mainstream levels as soon as 32GB HCDIMMs are released (they are currently in qualification with IBM/HP and have not been announced yet - though maybe expected shortly).

    I had created an infographic covering the memory choices - search the net for the article entitled:

    Infographic - memory buying guide for Romley 2-socket servers

    HCDIMMs are not available at SuperMicro (as they are for IBM/HP) - so I was surprised you even covered HCDIMMs (since the article is after all referring to the SuperMicro line of servers).
  • Casper42 - Friday, August 10, 2012 - link

    BTW, Johan, I work for HP and asked some of the guys in ISS Technical Marketing why we don't send you our servers for eval like you get from SuperMicro and sometimes Dell

    They felt that you guys didn't do alot of Server Reviews, and that your readership wasn't generally the kind of folks that buy HP Servers.

    So I am curious if you could spin up a poll or something in the future to prove them wrong.
    If there is enough support I'm sure we can you some gear to play with.

    I sometimes giggle when I see the stuff people on here get excited about in these reviews though. "Can you see the BIOS through IPMI?". Thats the kind of thing Compaq offered back with the RILOE II and have been integrated into the motherboard since iLO 1 which is like 4 or 5 years old at least.
    iLO4 on the Gen8 line have taken that a step further and we now hook the Display system BEFORE POST starts so instead of an invalid memory config getting you a series of beeps, you now get a full blown screen either on local VGA or on the Remote Console that straight up tells you you have a memory mismatch and why. i have seen his demo'd with NO DIMMs even installed in the server and you still get Video and obvious status messages.
  • Casper42 - Friday, August 10, 2012 - link

    Also you are about $2000 high on the HP SL unless I am missing something.
    I found these prices with QuickSpecs part numbers and Google, nothing magical inside HP.

    Half of one of these:
    Includes 8 fans and 3 PS

    2 of these
    2x2665 with 8GB

    Comes to about $11,600
  • JohanAnandtech - Tuesday, August 14, 2012 - link

    Hey Casper, contact me on my mail... thx! Reply
  • ad99 - Monday, April 1, 2013 - link

    You say:a quad rank DIMM with 4Gb chips is a 32GB DIMM (4 Gbit x 8 x 4 ranks),but I think 4 Gbit x 8 x 4 ranks make only 16GB,is that right? Reply
  • ad99 - Monday, April 1, 2013 - link

    No,4 Gbit x 8 x 4 ranks should be 128GB,not 32GB or 16GB,is that right? Reply

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