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JESD400-5D DDR5 SPD Explained: 9200 MT/s, SOCAMM2 & MRDIMM

The JEDEC JESD400-5D standard for DDR5 Serial Presence Detect (SPD) content is the essential framework for system firmware to configure and optimize DDR5 memory modules.

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This release, version 1.4, is a significant evolution, formally introducing support for data rates up to 9200 MT/s. But its scope extends far beyond speed.

It also standardizes the emerging SOCAMM2 form factor, defines the roles of critical on-module components like the SPD Hub and PMIC, refines server-grade error logging for MRDIMMs, and enhances security with robust write-protection mechanisms.

This article provides a detailed examination of these advancements, offering insight for system architects, engineers, and technology enthusiasts on the cutting edge of computing hardware. JESD400-5D: A Comprehensive Guide to the DDR5 SPD Standard

DDR5 Memory Standards

JESD400-5D: A Comprehensive Guide to the DDR5 SPD Standard

Exploring the latest standard for 9200 MT/s speeds, new form factors, on-module intelligence, and enhanced security. (Updated October 2025)

The Blueprint for Modern Memory

The JEDEC JESD400-5D standard for DDR5 Serial Presence Detect (SPD) content is the essential framework for system firmware to configure and optimize DDR5 memory modules. This release, version 1.4, is a significant evolution, formally introducing support for data rates up to 9200 MT/s. But its scope extends far beyond speed. It also standardizes the emerging SOCAMM2 form factor, defines the roles of critical on-module components like the SPD Hub and PMIC, refines server-grade error logging for MRDIMMs, and enhances security with robust write-protection mechanisms.

This article provides a detailed examination of these advancements, offering insight for system architects, engineers, and technology enthusiasts on the cutting edge of computing hardware.

Enabling 9200 MT/s: The Specs

The JESD400-5D standard explicitly details the SPD values required for modules to function at speeds up to DDR5-9200. This is accomplished through normative reference tables that module makers and BIOS developers use to ensure consistency.

Key Codifications:

  • Clock Period Definition: For DDR5-9200, the minimum average clock period, or $t_{CKAVGmin}$, is defined as 217 picoseconds (ps). This value is the foundation for all subsequent timing calculations.
  • Core Timing Parameters: The standard provides complete tables of primary timings like $t_{AA}$ (Access time), $t_{RCD}$ (Row Command Delay), and $t_{RP}$ (Row Precharge time) for all speed bins, including the new 9200 MT/s grade.
  • CAS Latency Support: Valid CAS Latency (CL) values are specified for each speed bin. This allows a memory controller to negotiate a stable and functional operating point with the memory module.

These comprehensive data sets create a clear standard for manufacturing and configuring modules at these high speeds, promoting broad interoperability across the hardware ecosystem.

The Rounding Algorithm: A Pillar of Stability

At 9200 MT/s, the clock period is just 217 picoseconds. At this scale, converting time-based parameters (in ps) into the integer number of clock cycles (nCK) a memory controller understands is a process where small errors can lead to major instability. A simple rounding mistake could violate a DRAM's timing requirement and cause a system crash. To prevent this, the standard mandates a specific rounding algorithm.

Timing Conversion Process

Nominal Time (ps)

Base parameter from SPD

Add 0.3% Margin

Preemptive stability buffer

Divide & Truncate

Convert to clock cycles

Final nCK Value

Stable, integer value

This standardized process adds a small timing margin (0.3%) before converting to clock cycles. This ensures that the final calculated value for the memory controller will always meet or exceed the DRAM's minimum timing requirement, preventing rounding errors and securing system stability.

New Form Factor: Welcoming SOCAMM2

A major addition in JESD400-5D is the formal SPD definition for the Small Outline Compression Attached Memory Module (SOCAMM2). This new, compact form factor is designed to replace traditional SO-DIMMs in laptops and small form-factor PCs. Its design offers significant advantages in space-saving and signal integrity, which is vital for achieving higher memory speeds in thin and light devices.

Form Factor Comparison: SOCAMM2 vs. SO-DIMM

SO-DIMM

  • Longer trace lengths from module to CPU, limiting top speeds.
  • Larger physical footprint on the motherboard.
  • Not easily adaptable for LPDDR memory types.

SOCAMM2

  • Direct compression mount shortens signal paths, improving high-speed stability.
  • Thinner profile and reduced board area, enabling sleeker device designs.
  • Versatile design that supports both standard DDR5 and low-power LPDDR5/5X.

The On-Module Ecosystem: SPD Hub and PMIC

Modern DDR5 modules are more than just DRAM chips; they are miniature ecosystems with their own intelligent components. The JESD400-5D standard formalizes SPD configurations for two key ICs: the SPD Hub and the Power Management IC (PMIC). The SPD Hub expands the functionality of the traditional SPD EEPROM, acting as a central point for configuration and also integrating a thermal sensor. The PMIC is responsible for regulating the specific voltages required by the DRAM chips on the module, improving power efficiency and stability.

Key On-Module Components

SPD Hub (with Thermal Sensor)

Acts as the module's brain. SPD bytes 330-332, for instance, define the manufacturer and revision of the hub, while other bytes configure the integrated thermal sensor's accuracy and resolution for precise temperature monitoring.

Power Management IC (PMIC)

Ensures stable power delivery. SPD bytes 335-336 identify the PMIC vendor and revision. This allows the host system to understand the module's power delivery capabilities and fine-tune system-level power management for optimal efficiency.

Configuration Integrity: SPD Write Protection

The data stored in the SPD EEPROM is critical for stable system operation. Any unauthorized or accidental modification can lead to performance issues, instability, or even prevent a system from booting. To combat this, the JEDEC standard defines a robust SPD Write Protection mechanism, detailed in Annex K.

Levels of SPD Write Protection

Revertible Write Protection

This mode offers a flexible security level. The SPD can be locked to prevent changes, but an authorized user with the correct high-voltage sequence can unlock it. This is useful for system integrators who may need to apply updates or custom configurations.

Permanent Write Protection (PWP)

Once engaged, this mode makes the SPD contents permanently read-only. This provides the highest level of security, ensuring that the module's factory-defined parameters can never be altered, which is critical for systems where long-term stability and consistency are non-negotiable.

SPD byte 0 is used to control and check the status of these write protection modes, giving system firmware a clear way to enforce configuration security.

Enhanced Error Logging for MRDIMMs

For enterprise and server environments, reliability is paramount. Multiplexer Rank DIMMs (MRDIMM) are a key technology for increasing memory capacity and bandwidth in servers. The JESD400-5D standard improves their reliability by enhancing error logging capabilities. Previously, identifying the precise location of an error on a high-density module could be ambiguous.

This update introduces a more granular error reporting mechanism by defining a bit for the "pseudo-channel" (PS). An MRDIMM operates with two 40-bit pseudo-channels. By explicitly identifying which pseudo-channel an error occurred on, the system can more accurately pinpoint a failing DRAM component, reducing diagnostic time and improving overall system serviceability.

MRDIMM Error Location Granularity

Previous Standard

Error reported at the rank level.

Ambiguity between two possible channels.

JESD400-5D Standard

Error reported with Pseudo-Channel (PS) identifier.

Precise location pinpoints the failing component.

The standard clarifies SPD byte `n+7`, bit 7, as the PS identifier for DRAM error logging, a crucial update for data center reliability.

Interactive Timing Comparison

An analysis of timing parameters across different speed grades reveals an important concept: while frequency scales, the physical time needed for certain DRAM operations remains fairly constant. This results in higher latencies when measured in clock cycles (nCK). Use the filters and chart below to see this relationship.

Filter by Speed Grade:

Speed Grade $t_{CKmin}$ (ps) $t_{AA}$ (ps) $t_{AA}$ (nCK) $t_{RCD}$ (ps) $t_{RCD}$ (nCK)

Bandwidth vs. Latency Visualization

This chart illustrates that as bandwidth (MT/s) increases, the command latencies in clock cycles (nCK) also rise, even though the absolute time in picoseconds remains stable.

Frequently Asked Questions

What is the primary benefit of the DDR5-9200 speed grade?

The main advantage is a significant increase in memory bandwidth. This allows the CPU to access data much faster, which is highly beneficial for data-intensive applications like AI model training, high-resolution video editing, scientific simulations, and extreme gaming.

Why was the SOCAMM2 module developed?

SOCAMM2 was created to overcome the physical and electrical limitations of the aging SO-DIMM standard in modern thin-and-light laptops. Its compression-mount design shortens the electrical pathways to the CPU, improving signal integrity for higher speeds. It also saves valuable motherboard space and supports both DDR5 and LPDDR5 memory types on the same connector design.

What does the on-module PMIC actually do?

The Power Management IC (PMIC) is responsible for taking the main voltage supplied to the memory module and converting it into the precise, stable, and lower voltages required by the DRAM chips themselves (e.g., VDD, VDDQ, VPP). Moving voltage regulation from the motherboard directly onto the DIMM results in cleaner power delivery and better energy efficiency.

Can I accidentally corrupt my memory's configuration settings?

It's highly unlikely on modern modules. The SPD Write Protection features are designed to prevent this. Most consumer modules will have revertible protection, but mission-critical or enterprise-grade modules may use Permanent Write Protection (PWP), which makes the SPD's configuration data read-only for the life of the module, ensuring its settings can never be altered.

How does improved MRDIMM logging benefit data centers?

In a server with dozens or hundreds of memory modules, quickly identifying a single failing chip is crucial for minimizing downtime. By adding a "pseudo-channel" identifier to error logs, the system can pinpoint the exact location of a fault on a high-density MRDIMM. This precision allows technicians to replace the correct component quickly, enhancing system reliability and serviceability.

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