Micron's official DDR5 module example is MTC40F2046S1RC48BA1T. Read it as MT | C | 40 | F | 2 | 0 | 4 | 6 | S | 1 | R | C | 48B | A | 1 | T. Those fields identify the manufacturer, DDR generation, DRAM count, module power class, physical and logical ranks, component organization, capacity, height, die stacking, module type, temperature capability, speed bin, die revision, PCB revision and optional shipment pack.
That is a module ordering code, not a DRAM-component code. A buyer should not decode it with the shorter MT40A component pattern used for standalone DDR4 ICs. For a server or workstation BOM, every field in the module string matters because two DDR5 modules can share capacity and data rate while differing in rank structure, bus width, register type, temperature capability or SPD data.
Open the full-size Micron DDR5 module ordering diagram and zoom.
Decode the Micron DDR5 module code field by field #
| Field | Official example | Buyer interpretation |
|---|---|---|
| Manufacturer | MT | Micron Technology |
| Product family | C | DDR5 SDRAM module family |
| Number of DRAM die | 40 | Forty DRAM die on the module |
| Voltage | F | 12 V RDIMM module-power class in the numbering guide |
| Package ranks | 2 | Two physical package ranks |
| Logical ranks | 0 | No additional 3DS or width-buffer logical-rank multiplier |
| Component configuration | 4 | x4 DRAM organization |
| Module density | 6 | 64 GB module capacity |
| Module height | S | Low-profile module |
| Die-in-package | 1 | Single-die package |
| Module type | R | 288-pin or 287-pin RDIMM, x80 bus width |
| Temperature capability | C | Commercial-temperature capability code |
| Module speed | 48B | DDR5-4800B, 2400 MHz clock, 4800 MT/s, CL40-39-39 |
| Die revision | A | Part-mark die revision designator |
| PCB revision | 1 | Numeric production-board revision |
| Final pack type | T | Optional tray shipment code for CPG distribution parts |
The voltage character deserves special attention. In this module guide, F means the 12 V input class used by RDIMMs; it does not mean the DRAM I/O voltage. Micron's current product page for MTC40F2046S1RC64BH1 separately lists 1.1 V I/O. Treat module input power and memory-interface I/O voltage as different specifications.
Micron's official syntax example ends in T so the optional shipment field is visible. The current production RDIMM MTC40F2046S1RC64BH1 does not carry that optional final character. Its official product record identifies a 64 GB, x80, ECC, DDR5 RDIMM with forty components, 6400 MT/s, CL52, commercial 0°C to +95°C operation and production status. The two strings are useful together: the guide proves what each position means, while the live catalogue proves that omitted optional packaging characters and newer speed or revision fields occur in real orderable parts.
Rank, organization and density are separate decisions #
The sequence 2 | 0 | 4 | 6 is not one capacity code. It says two package ranks, no extra logical ranks, x4 component organization and 64 GB module density. The guide permits package-rank codes for one, two, three, four and eight ranks. Logical-rank codes cover none or total logical-rank counts of two, four, eight or sixteen for 3DS or width-buffer designs.
Changing one field can alter the load seen by the memory controller even when capacity stays at 64 GB. A replacement screen therefore needs the host platform's supported rank topology as well as the advertised capacity. Likewise, x4, x8 and x16 component configurations are not interchangeable descriptions of the same module; they affect how the capacity and ECC path are built.
The density field spans 8 GB through 4096 GB in the numbering guide, using numeric and alphabetic codes. The live Micron RDIMM catalogue is narrower and status-dependent: it currently exposes production, sampling and end-of-life rows separately. A code's theoretical presence in the numbering guide does not prove that a matching module is in production.
Module type fixes the mechanical and bus-width boundary #
| Code | Official module description | Procurement boundary |
|---|---|---|
| S | 262-pin SODIMM, x64 | Unbuffered small-outline module |
| V | 262-pin CSODIMM, x64 | Clocked small-outline module |
| T | 262-pin SOEDIMM, x72 | ECC small-outline module |
| W | 262-pin CSODIMM, x72 | Clocked ECC small-outline module |
| U | 288-pin UDIMM, x64 | Unbuffered full-size module |
| A | 287-pin CUDIMM, x64 | Clocked unbuffered module |
| E | 288-pin EUDIMM, x72 | ECC unbuffered module |
| B | 287-pin CUDIMM, x72 | Clocked ECC module |
| R | 288-pin or 287-pin RDIMM, x80 | Registered server module |
| P | 288-pin or 287-pin RDIMM, x72 | Registered ECC-width module |
The asterisked module types in Micron's guide use a die-count increment of ten rather than nine. That note is part of the official decoder and is another reason not to rebuild an OPN from a marketing description.
The height code adds another mechanical gate: S is low profile, D is very low profile, H is 2U and L is 4U. Those labels do not supply a complete mechanical drawing. Confirm the exact module outline and connector keying from the part-specific document before approving a chassis or heat-spreader change.
An RDIMM is not a drop-in substitute for a UDIMM or CUDIMM merely because the connector family and DDR generation look similar. The register or clock-driver architecture, pin definition, bus width and platform support remain explicit compatibility checks.
Speed bin and SPD must agree with the platform #
The speed field combines the JEDEC speed class, module clock, data rate and timing set. Examples from the official guide include:
| Code | JEDEC bin | Clock | Data rate | CL-nRCD-nRP |
|---|---|---|---|---|
| 48B | DDR5-4800B | 2400 MHz | 4800 MT/s | 40-39-39 |
| 56B | DDR5-5600B | 2800 MHz | 5600 MT/s | 46-45-45 |
| 64B | DDR5-6400B | 3200 MHz | 6400 MT/s | 52-52-52 |
| 80B | DDR5-8000B | 4000 MHz | 8000 MT/s | 64-64-64 |
A faster code is not an automatic purchasing upgrade. The server CPU, board topology, BIOS, channel population and module rank structure all participate in the supported data rate. Micron's SPD lookup page states that a system BIOS may depend on module SPD data to configure and optimize the memory subsystem. The safest alternate screen therefore checks the exact module OPN in the SPD tool or part information page and then confirms the platform qualification list.
Do not infer a temperature range from the letter alone when the product record is available. The guide defines C, I and B as commercial, industrial and extended capability codes, while the current MTC40F2046S1RC64BH1 page gives the exact 0°C to +95°C range for that part. The part-level record controls the RFQ specification.
Controlled alternate-screening workflow #
Keep a proposed alternate on hold until all of these conditions are answered:
- Match the complete module type, connector and bus-width code; R, P, U and A are different module contracts.
- Match capacity, package ranks, logical ranks and component organization, not capacity alone.
- Confirm module input class and I/O voltage as separate specifications.
- Check height, die-in-package construction and any thermal or airflow constraint.
- Verify the speed bin, timing set and SPD data against the target platform and populated-channel configuration.
- Confirm temperature capability, die revision and PCB revision through the exact part record or change documentation.
- Treat a missing or added R/T shipment character as a logistics difference only after the electrical OPN and required pack quantity are established.
- Record production, sampling or end-of-life status from the live catalogue on the date of purchase review.
For RFQ work, send the full Micron module OPN, target quantity, acceptable speed and temperature range, required module type, rank structure, host platform and packaging expectation. A request for “64 GB DDR5” is not specific enough to preserve compatibility.
Conclusion #
Micron's DDR5 module number carries sixteen procurement fields. The official example MTC40F2046S1RC48BA1T identifies far more than capacity and speed: it fixes rank topology, component width, module height, die stacking, RDIMM bus width, temperature capability, revisions and shipment pack. Use the official decoder to interpret the string, the current part page to confirm exact specifications and lifecycle state, and the SPD or platform qualification data to judge substitution. Matching only 64 GB and 4800 or 6400 MT/s is not a safe module replacement method.
Official references #
- Micron Module Part Numbering Guide — DDR5, DDR4 and legacy module systems
- Micron RDIMM product page and module resources
- Micron RDIMM part catalogue
- Micron MTC40F2046S1RC64BH1 production-part record
- Micron serial presence-detect part-number lookup
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