HMA81GS6AFR8N-UH SO-DIMM Design-In Guide

The HMA81GS6AFR8N-UH is an 8GB SK hynix DDR4 SO-DIMM for a host designed to accept unbuffered, non-ECC memory. Selecting it for a compact computer requires three separate decisions: whether the host supports its organization, whether the board and enclosure meet electrical and thermal requirements, and whether the purchased module matches the approved configuration.

This guide focuses on those design-in decisions. A speed label alone cannot establish compatibility with a laptop, embedded board or appliance.

Identify the module before designing the socket

The manufacturer's ordering and speed-grade tables identify the UH variant as follows. The x64 entry is non-ECC; ECC entries elsewhere in this family document refer to other module variants.

See the SK hynix ordering table and speed-grade table, hosted by Geizhals.

For a purchasing specification, retain the entire HMA81GS6AFR8N-UH string. Request a readable label and an SPD record for the proposed supply, including any additional label codes. Do not silently substitute a different die revision, rank organization or speed suffix because the capacity matches.

Check the host in a defined configuration

Start with the processor's memory-controller documentation, the board manual and its approved-memory list. Confirm support for unbuffered DDR4 SO-DIMMs, 8Gb x8 DRAM organization, capacity per slot and the intended number of populated slots. Record the BIOS or firmware revision used for qualification.

A controller advertised for DDR4-2666 still needs to support the proposed module and its SPD settings. A lower operating rate may be selected during initialization, but successful training and operation depend on the complete platform. Likewise, two modules with the same nominal capacity and rate can differ in organization and firmware acceptance.

Keep a configuration record covering the board revision, processor, socket population, module labels and negotiated memory rate. For an existing system upgrade, obtain the OEM's memory requirements before ordering. For a new board, define the acceptance configuration before buying production quantities.

Use a host-specific electrical design

The module lists nominal VDD/VDDQ of 1.2V, VPP of 2.5V and VDDSPD of 2.25–3.6V. The specified VDD/VDDQ operating interval is 1.14–1.26V. Check the complete supply conditions in the module features and DC operating conditions.

Separate the command/address reference, VREFCA, from the DRAM data reference. DDR4 provides internal DQ reference generation; the module does not require the generic external VREFDQ rail sometimes shown in older memory design discussions. The functional descriptions identify internal DQ Vref, and the 8GB x64 block diagram shows the relevant module interfaces.

Map the connector against the correct module drawing and the controller reference design. Review SPD communication, reset, reference supplies, termination and power sequencing together. Size regulators and decoupling from the applicable current conditions and the host power budget. A list of capacitor values cannot replace a power-integrity analysis.

Derive trace impedance, byte-lane matching, clock routing and termination from the chosen controller and board stack-up. Include the socket and module loading in signal-integrity work. Avoid adopting a universal routing tolerance or copying a multi-slot topology into a different design.

Budget bandwidth without promising application speed

At an assumed 2400 million transfers per second across one 64-bit data channel, the arithmetic ceiling is 2400 × 10⁶ × 64 ÷ 8 = 19.2 × 10⁹ bytes per second, or 19.2 GB/s in decimal units. This calculation assumes continuous data transfers and excludes refresh, command overhead, turnaround and access-pattern effects.

Use that ceiling only as an initial planning input. Measure the actual application on the intended platform, especially when CPU and graphics share memory traffic. A 1Rx8 organization does not by itself prove lower system power or faster execution than a dual-rank configuration. Compare qualified configurations using the same workload, firmware and thermal conditions.

Validate temperature at the DRAM case

The datasheet specifies a normal DRAM case range of 0–85°C and a conditional 85–95°C extended range. The latter requires appropriate refresh and self-refresh behavior, with SPD options considered. These are component case temperatures, not enclosure ambient ratings. See the manufacturer's temperature conditions.

For a fanless enclosure, define the maximum ambient condition, nearby heat sources, airflow and workload before qualification. Measure case temperature with an appropriate method and verify that firmware implements the required temperature behavior. A thermal sensor reading can assist monitoring, but it should not be treated as an automatic measurement of every DRAM package's hottest case point.

Do not classify this module as suitable for subzero operation or a harsh industrial environment from the SO-DIMM format or brand alone. Mechanical clearance, vibration retention and environmental requirements need their own evidence.

Build an acceptance plan that purchasing can use

1. Identity: compare labels and SPD information with the approved module record; investigate inconsistent capacity, organization or suffix details.
2. Startup: exercise cold starts, warm resets and any supported sleep/resume states on the intended firmware.
3. Memory operation: test the supported slot populations and application workload; record errors and actual negotiated settings.
4. Environment: assess the assembled system at its defined thermal and mechanical limits.
5. Supply agreement: document condition, quantity, traceability information and permitted substitutions in the quotation and purchase requirements.

These steps define a qualification workflow; results must come from the buyer's actual platform. For sourcing, search the exact module number and request confirmation of the proposed lot. A catalog result does not establish stock, lead time, lifecycle status or host approval.

Technical reference: SK hynix, DDR4 SDRAM SO-DIMM Based on 8Gb A-die, Rev. 1.4, September 2017, manufacturer-authored document hosted by Geizhals. The revision date identifies this document edition; it does not establish the exact module's commercial launch date.