Samsung M425R1GB4BB0 DDR5 Memory: Power Efficiency & Performance

What Is M425R1GB4BB0? The "GB4" Does Not Mean 4 Gigabytes — and the "1Rx16" Tells You More About Performance Than Any Speed Spec

Two things in the M425R1GB4BB0 part number are commonly misread, and both affect how this module should be specified and evaluated.

The first: GB4 does not mean 4 gigabytes. In Samsung's module naming convention, "GB" here encodes the die density and die width — specifically 8 Gb (8 gigabit) per die, with x16 organization per die (4 chips across the 64-bit DDR5 data bus). The "4" in GB4 refers to the number of die packages on the module, not to gigabytes of capacity. The module's actual capacity is 8 gigabytes — derived from 4 chips × 8 Gb = 32 Gb / 8 bits = 4 GB per half, × 2... or more precisely from the complete 1024M × 64-bit organization. The marketing label and the actual capacity match, but the path from the part number to that capacity requires understanding what GB4 actually encodes.

The second: 1Rx16 matters more for performance than the DDR5-4800 speed rating. In a 1Rx16 SO-DIMM, each chip is x16 wide, and there is only one rank. The entire 64-bit DDR5 bus is served by 4 chips in a single rank. By contrast, a 2Rx8 SO-DIMM uses 16 chips arranged in two ranks of 8 chips each — each chip contributing 8 bits to the 64-bit bus. The 2Rx8 configuration allows rank interleaving, where the memory controller can issue commands to Rank 0 while Rank 1 is precharging, dramatically improving sustained memory bandwidth. Two SO-DIMMs at identical DDR5-4800 speed will not perform identically if one is 1Rx16 and the other is 2Rx8.

M425R1GB4BB0 is a 1Rx16 module. Whether this matters for a given application depends on the workload. Understanding what 1Rx16 means — and when it matters — is what allows this module to be specified correctly rather than selected by price alone.

1.0 Full Part Number Decoded: M425R1GB4BB0

Samsung module part numbers encode the product family, form factor, rank, die configuration, die revision, speed grade, and packaging in a structured string:

M — Samsung memory module product prefix (M = module; distinct from K = individual die chip)

4 — Memory technology generation indicator within Samsung's module naming (maps to DDR5 in this series)

25 — Form factor code: 25 = 262-pin SO-DIMM (Small Outline DIMM for laptops and compact systems). Compare: 32 = 288-pin UDIMM (desktop), 32R = 288-pin RDIMM (server).

R — Memory type: R = SDRAM (standard DRAM, not NVDIMM or other specialty type)

1 — Rank count: 1 = Single rank (1R). The entire module serves as one logical memory rank; all chips on the module respond to the same chip-select signal.

GB4 — Die configuration code:

• G = die density tier (maps to 8 Gb per die in this context)
• B = die data width tier (maps to x16 width per die — each die presents 16 data bits)
• 4 = number of die packages on the module (4 dies total)
• Combined: 4 dies × 8 Gb each = 32 Gb total raw; organized as 1024M × 64-bit = 8 GB per module

B — Die revision: B = second die revision within the DDR5 8 Gb x16 product family (first revision was A)

B0 — Speed/revision bin code within the B die family

Ordering suffix (after the dash):

Suffix	Speed	Timing	Notes
-CQK	DDR5-4800 (PC5-38400)	CL40	Base speed, most common
-CWM	DDR5-5600 (PC5-44800)	CL46	Higher speed variant
-CQKOL	DDR5-4800	CL40	OEM-locked variant

The suffix characters encode: C = commercial temperature; Q/W = speed bin group; K/M = specific timing bin; additional characters for OEM or packaging variants.

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2.0 Specifications and What the Numbers Mean

Confirmed specifications from distributor data and Samsung product page:

• Capacity: 8 GB per module
• DDR generation: DDR5
• Speed grade (-CQK): DDR5-4800 (PC5-38400)
• Peak bandwidth: 4,800 MT/s × 8 bytes = 38,400 MB/s (38.4 GB/s) peak per module
• Primary timings (CQK): CL40-39-39-77 (CAS Latency 40, tRCD 39, tRP 39, tRAS 77 cycles)
• Absolute CAS latency: CL40 at 4800 MT/s → tCK = 1/2400 MHz = 0.4167 ns → tCL = 40 × 0.4167 ns = 16.67 ns
• Operating voltage: 1.1V (DDR5 standard — lower than DDR4's 1.2V)
• Form factor: 262-pin SO-DIMM
• Rank configuration: 1Rx16 (single rank, x16 die width)
• Module organization: 1024M × 64-bit
• ECC: Non-ECC (standard consumer/laptop module)
• On-Die ECC: Yes (DDR5 internal feature — see Section 3)
• SPD (Serial Presence Detect): Yes, EEPROM on module for auto-configuration

Speed comparison for the M425R1GB4BB0 family:

Suffix	Speed	Peak BW	CL	Absolute tCL	VDD
-CQK	DDR5-4800	38.4 GB/s	40	16.67 ns	1.1V
-CWM	DDR5-5600	44.8 GB/s	46	16.43 ns	1.1V

Note: the absolute CAS latency (in nanoseconds) is similar between the two speeds because the higher data rate runs a faster clock — higher CL number but nearly identical nanosecond latency.

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3.0 What Is New in DDR5: Sub-Channels, On-Die ECC, and the VPP Rail

DDR5 is not simply faster DDR4. Several architectural changes affect how it is designed with and how it behaves in the system, and M425R1GB4BB0 implements all of them:

Sub-channel architecture:

DDR4's 64-bit data bus operates as one wide channel. DDR5 splits this into two independent 32-bit sub-channels within a single DIMM slot. Each sub-channel has its own command/address bus, its own data bus, and its own independent operation. The memory controller can issue independent commands to each sub-channel — for example, reading from sub-channel 0 while sub-channel 1 executes a precharge. This sub-channel independence, combined with the higher per-pin data rate, gives DDR5 substantially higher sustained bandwidth than DDR4 at equivalent clock frequencies.

For the M425R1GB4BB0's 4 chips organized as 1Rx16: 2 chips serve sub-channel 0 (each contributing 16 bits = 32 bits total per sub-channel), and 2 chips serve sub-channel 1. The two sub-channels operate independently, enabling the memory controller to pipeline operations across both halves.

On-Die ECC (ODECC):

All DDR5 devices include on-die ECC — a hardware error correction circuit inside each DRAM die that detects and corrects single-bit errors within the die's internal array before the data is sent to the memory bus. This is not the same as system-level ECC (which requires ECC DIMM + ECC-capable memory controller). On-die ECC is transparent to the memory controller and provides data integrity improvement within the die without any change to the external interface. The M425R1GB4BB0 is a Non-ECC module (no extra bits on the module-level data bus), but its internal die-level ODECC operates regardless.

VPP — the new supply rail:

Like DDR4, DDR5 requires a VPP supply rail (2.5V) in addition to VDD/VDDQ (1.1V). This VPP rail was not present in DDR3 or earlier. System designers migrating from DDR4 to DDR5 do not need to add VPP (DDR4 also required it), but designers moving from DDR3 must add this supply rail.

DDR5 additionally introduces an on-DIMM voltage regulator (PMIC — Power Management IC) for server RDIMM applications. SO-DIMMs like M425R1GB4BB0 do not typically include a PMIC; the host platform provides the regulated VDD/VDDQ directly.

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4.0 The Real Performance Difference: 1Rx16 vs 2Rx8

This is the most practically significant technical detail about M425R1GB4BB0 that is invisible from the marketing specifications.

What 1Rx16 means physically:

The M425R1GB4BB0 has 4 DDR5 die packages on the PCB. Each die is an x16 device — it contributes 16 data bits to the module's 64-bit bus (2 sub-channels × 32 bits each = 64 bits). All 4 dies share one chip-select signal (one rank). When the memory controller issues a command, all 4 dies respond simultaneously as a single unit.

What 2Rx8 means physically (comparison):

A hypothetical 8GB DDR5 SO-DIMM in 2Rx8 configuration would have 16 die packages — 8 per rank, each contributing 8 bits. The two ranks have independent chip-select signals. The memory controller can address Rank 0 and Rank 1 alternately in a pipelined fashion.

Why rank interleaving matters for bandwidth:

A DRAM row access cycle requires: ACTIVATE (open a row) → CAS READ/WRITE (access columns) → PRECHARGE (close the row). The precharge step takes time — the row cannot be accessed again until it completes. With a single rank, the memory controller must wait for precharge before issuing another row activation to the same bank.

With two ranks, while Rank 0 is precharging, Rank 1 can be activating and reading. The controller can alternate between ranks, keeping the data bus busy during the idle-wait periods. In bandwidth-intensive workloads, this rank interleaving can improve sustained bandwidth by 10–30% compared to a single-rank configuration at the same DDR5 speed grade.

When does 1Rx16 matter in practice?

For most laptop workloads — office applications, web browsing, document editing, moderate gaming — the memory subsystem is rarely bandwidth-limited, and the difference between 1Rx16 and 2Rx8 is not perceptible. For workloads that are genuinely memory-bandwidth bound — video editing with large raw files, machine learning inference, scientific simulation — the 2Rx8 configuration's rank interleaving advantage becomes measurable. For embedded applications using DDR5 SO-DIMM in a single-board computer or industrial compute module where consistent memory throughput matters, verify whether the application workload is bandwidth-bound before specifying 1Rx16 as the lower-cost option.

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5.0 Five Misconceptions About This Module

Misconception 1: "GB4 means 4 GB"

The most common misreading. GB4 in Samsung's module naming is a die configuration code — 8 Gb die × 4 packages = 32 Gb = 4 GB per 32-bit half-channel, but 8 GB total across the full 64-bit bus. The full capacity is encoded in the combination of die density (G = 8 Gb), die width (B = x16), and die count (4), organized across the full 64-bit module width. The resulting 8 GB capacity matches the marketing label, but reading "GB4" as "4 GB" misunderstands what each field encodes.

Misconception 2: "DDR5-4800 CL40 has higher latency than DDR4-3200 CL22"

In clock cycles, CL40 > CL22. In absolute time: DDR5-4800 CL40 → tCL = 40/(4800/2) = 40/2400 = 16.67 ns. DDR4-3200 CL22 → tCL = 22/1600 = 13.75 ns. DDR5-4800 has approximately 2.9 ns more first-access latency than DDR4-3200. However, DDR5's dramatically higher bandwidth more than compensates in throughput-bound workloads. For latency-critical workloads (pointer-chasing memory access patterns in databases), this extra 2.9 ns per access is meaningful; for sequential or streaming workloads, the bandwidth advantage of DDR5 dominates.

Misconception 3: "Non-ECC means no error correction in this module"

Non-ECC refers to the system-level ECC interface — the module has no extra bits on its external data bus for system ECC (which would require a 72-bit bus instead of 64-bit, and an ECC-capable memory controller). However, all DDR5 dies include on-die ECC (ODECC) that operates internally within each chip, correcting single-bit errors within the die before data reaches the bus. This internal correction is present in M425R1GB4BB0 regardless of the "Non-ECC" label, and provides a meaningful reliability improvement over DDR4 (which had no on-die ECC). For applications requiring full system-level ECC, an ECC SO-DIMM and ECC-capable platform are still needed.

Misconception 4: "M425R1GB4BB0-CQK and M425R1GB4BB0-CWM can be mixed in a dual-channel system"

The -CQK (DDR5-4800) and -CWM (DDR5-5600) variants are the same die at different speed bins. Mixing them in a dual-channel system (two SO-DIMM slots) forces the memory controller to operate both modules at the lower speed (DDR5-4800). This is functionally acceptable but wastes the CWM's higher speed capability. For optimal performance, use matched pairs in the same speed grade. Matching is more important for dual-channel throughput than absolute speed — two matched CQK modules operating in dual-channel mode will outperform mismatched CQK+CWM running at the lower speed with potential timing inconsistencies.

Misconception 5: "DDR5 SO-DIMM fits in DDR4 SO-DIMM slots"

DDR5 and DDR4 SO-DIMMs have different key notch positions and different pin counts (DDR5: 262 pins; DDR4: 260 pins). DDR5 SO-DIMMs physically cannot be inserted into DDR4 SO-DIMM slots, and vice versa. The different notch position is an intentional mechanical lockout. Attempting to force a DDR5 module into a DDR4 slot risks damaging the module and the slot. Always verify the DDR generation supported by the platform before ordering memory.

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6.0 Practice Problems

Problem 1: An M425R1GB4BB0-CQK runs at DDR5-4800 with CL40. What is the actual CAS latency in nanoseconds? Compare to DDR3-1600 CL11. (Answer: DDR5 tCL = 40 / 2400 MHz = 16.67 ns. DDR3 tCL = 11 / 800 MHz = 13.75 ns. DDR5-4800 has ~2.9 ns more first-access latency than DDR3-1600, despite the 3× higher data rate.)

Problem 2: A laptop supports dual-channel DDR5 with two SO-DIMM slots. You install one 8GB M425R1GB4BB0-CQK (1Rx16) and one 16GB DDR5-4800 SO-DIMM (2Rx8). Does this system run in dual-channel mode? (Answer: Depends on the platform. Most modern memory controllers support asymmetric dual-channel (flex mode), where the first 8GB of each module runs in dual-channel, and the remaining 8GB of the 16GB module runs in single-channel. Check the platform's memory configuration guide for the specific behavior.)

Problem 3: What is the peak theoretical bandwidth of two M425R1GB4BB0-CQK modules in a dual-channel DDR5 configuration? (Answer: Each module: 38.4 GB/s. Dual-channel doubles the bus width (2 × 64 bits = 128 bits), so peak bandwidth = 38.4 × 2 = 76.8 GB/s. This compares to ~51.2 GB/s for dual-channel DDR4-3200.)

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7.0 Real Questions from System Builders and Engineers

Q: The M425R1GB4BB0-CQK is listed as "1Rx16" but a competing 8GB DDR5 SO-DIMM is listed as "2Rx8." Both are DDR5-4800. Which should I choose for a video editing workstation laptop?

A: For video editing — which involves reading large sequential blocks of compressed video data and writing large output files — memory bandwidth matters more than latency. The 2Rx8 configuration's rank interleaving delivers higher sustained bandwidth in sequential workloads, typically 10–20% higher than 1Rx16 at the same DDR5 speed. If the laptop platform supports both configurations (verify compatibility), the 2Rx8 module will provide measurably better throughput in bandwidth-intensive video editing scenarios. The 1Rx16 (M425R1GB4BB0) is typically lower cost and adequate for general-purpose use; for a dedicated workstation use case, the 2Rx8 variant is the better technical choice if available.

Q: I upgraded my laptop from DDR4-3200 16GB to two M425R1GB4BB0-CQK (16GB total DDR5-4800) and it actually feels slower in some scenarios. How is that possible?

A: The most likely explanation is that you moved from a 2Rx8 or larger DDR4 configuration to 1Rx16 DDR5 — gaining bandwidth in some scenarios but losing rank interleaving that the DDR4 had. Additionally, DDR5's first-access latency (16.67 ns at CL40) is higher than DDR4-3200 (13.75 ns at CL22). For workloads dominated by pointer-chasing (database traversals, some gaming scenarios with large asset streaming), the higher latency is noticeable despite the higher bandwidth. Finally, confirm the system is running in dual-channel mode (two modules installed in the correct slots) — single-channel DDR5 can be slower than dual-channel DDR4 in bandwidth-sensitive workloads.

Q: We are designing an industrial compute module using DDR5 SO-DIMM. Is M425R1GB4BB0-CQK available in industrial temperature grade?

A: The standard M425R1GB4BB0-CQK is rated for commercial temperature (typically 0°C to +85°C case temperature, as is standard for SO-DIMM modules). For industrial temperature requirements (−40°C to +85°C or beyond), Samsung offers specific industrial-grade DDR5 SO-DIMM variants with extended temperature qualification — these typically carry different suffix codes indicating industrial temperature screening. For industrial embedded designs, explicitly request industrial temperature grade SO-DIMMs from Samsung's authorized distribution or engage Samsung Semiconductor's embedded DRAM product line directly. Do not use commercial-temperature SO-DIMMs in applications that experience sub-0°C ambient temperatures without verifying that the platform and memory have been tested and qualified at those temperatures.

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8.0 Quick Reference Card

Part Number Decode:

Field	Value	Meaning
M	M	Samsung memory module
4	4	DDR5 generation indicator
25	25	262-pin SO-DIMM
R	R	SDRAM type
1	1	Single rank (1R)
GB4	GB4	4 × 8Gb x16 dies = 8GB total
B	B	Die revision B
B0	B0	Speed/stepping bin

Suffix Speed Comparison:

Suffix	Speed	Timing	Peak BW	Absolute tCL
-CQK	DDR5-4800	CL40	38.4 GB/s	16.67 ns
-CWM	DDR5-5600	CL46	44.8 GB/s	16.43 ns

1Rx16 vs 2Rx8 — Performance Impact:

Configuration	Chips	Rank interleaving	BW advantage	Best for
1Rx16 (this module)	4 × x16	None	—	General use, cost-optimized
2Rx8	16 × x8	Yes	+10–30%	Bandwidth-intensive workloads

DDR5 New Features vs DDR4:

Feature	DDR5	DDR4
Sub-channels	2 × 32-bit	1 × 64-bit
On-die ECC	Yes (internal)	No
VDD/VDDQ	1.1V	1.2V
Pin count (SO-DIMM)	262	260
Physical compatibility	Not compatible	Not compatible

The Key Math: GB4 → 8GB 4 dies × 8 Gb/die = 32 Gb ÷ 8 = 4 GB per 32-bit sub-channel × 2 sub-channels = 8 GB total

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For sourcing Samsung M425R1GB4BB0 DDR5 SO-DIMM with verified authenticity and competitive pricing, visit aichiplink.com.

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Written by Jack Elliott from AIChipLink.

 

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