Feed: AnandTech
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Title: JEDEC Plans LPDDR6-Based CAMM, DDR5 MRDIMM Specifications

Date: Tue, 23 Jul 2024 19:00:00 EDT
Link: https://www.anandtech.com/show/21487/jedec-pl...

Following a relative lull in the desktop memory industry in the previous
decade, the past few years have seen a flurry of new memory standards and
form factors enter development. Joining the traditional DIMM/SO-DIMM form
factors, we've seen the introduction of space-efficient DDR5 CAMM2s, their
LPDDR5-based counterpart the LPCAMM2, and the high-clockspeed optimized
CUDIMM. But JEDEC, the industry organization behind these efforts, is not
done there. In a press release sent out at the start of the week, the group
announced that it is working on standards for DDR5 Multiplexed Rank DIMMs
(MRDIMM) for servers, as well as an updated LPCAMM standard to go with next-
generation LPDDR6 memory.

Just last week Micron introduced the industry's first DDR5 MRDIMMs, which are
timed to launch alongside Intel's Xeon 6 server platforms. But while Intel
and its partners are moving full steam ahead on MRDIMMs, the MRDIMM
specification has not been fully ratified by JEDEC itself. All told, it's not
unusual to see Intel pushing the envelope here on new memory technologies
(the company is big enough to bootstrap its own ecosystem). But as MRDIMMs
are ultimately meant to be more than just a tool for Intel, a proper industry
standard is still needed - even if that takes a bit longer.

Under the hood, MRDIMMs continue to use DDR5 components, form-factor, pinout,
SPD, power management ICs (PMICs), and thermal sensors. The major change with
the technology is the introduction of multiplexing, which combines multiple
data signals over a single channel. The MRDIMM standard also adds RCD/DB
logic in a bid to boost performance, increase capacity of memory modules up
to 256 GB (for now), shrink latencies, and reduce power consumption of high-
end memory subsystems. And, perhaps key to MRDIMM adoption, the standard is
being implemented as a backwards-compatible extension to traditional DDR5
RDIMMs, meaning that MRDIMM-capable servers can use either RDIMMs or MRDIMMs,
depending on how the operator opts to configure the system.

The MRDIMM standard aims to double the peak bandwidth to 12.8 Gbps,
increasing pin speed and supporting more than two ranks. Additionally, a
"Tall MRDIMM" form factor is in the works (and pictured above), which is
designed to allow for higher capacity DIMMs by providing more area for laying
down memory chips. Currently, ultra high capacity DIMMs require using
expensive, multi-layer DRAM packages that use through-silicon vias (3DS
packaging) to attach the individual DRAM dies; a Tall MRDIMM, on the other
hand, can just use a larger number of commodity DRAM chips. Overall, the Tall
MRDIMM form factor enables twice the number of DRAM single-die packages on
the DIMM.

Meanwhile, this week's announcement from JEDEC offers the first significant
insight into what to expect from LPDDR6 CAMMs. And despite LPDDR5 CAMMs
having barely made it out the door, some significant shifts with LPDDR6
itself means that JEDEC will need to make some major changes to the CAMM
standard to accommodate the newer memory type.

JEDEC Presentation: The CAMM2 Journey and Future Potential

Besides the higher memory clockspeeds allowed by LPDDR6 - JEDEC is targeting
data transfer rates of 14.4 GT/s and higher - the new memory form-factor will
also incorporate an altogether new connector array. This is to accommodate
LPDDR6's wider memory bus, which sees the channel width of an individual
memory chip grow from 16-bits wide to 24-bits wide. As a result, the current
LPCAMM design, which is intended to match the PC standard of a cumulative 128-
bit (16x8) design needs to be reconfigured to match LPDDR6's alterations.

Ultimately, JEDEC is targeting a 24-bit subhannel/48-bit channel design,
which will result in a 192-bit wide LPCAMM. While the LPCAMM connector itself
is set to grow from 14 rows of pins to possibly as high as 20. New memory
technologies typically require new DIMMs to begin with, so it's important to
clarify that this is not unexpected, but at the end of the day it means that
the LPCAMM will be undergoing a bigger generational change than what we
usually see.

JEDEC is not saying at this time when they expect either memory module
standard to be completed. But with MRDIMMs already shipping for Intel systems
- and similar AMD server parts due a bit later this year - the formal version
of that standard should be right around the corner. Meanwhile, LPDDR6 CAMMs
will be a bit farther out, particularly as the memory standard itself is
still under development.

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