1. Physical Interface Specifications - The MMRD4 series adopts the standard SDHC form factor (32mm × 24mm × 2.1mm), while the MURD4 series uses the microSD form factor (15mm × 11mm × 1mm). - If the original design has a fixed SD card slot footprint, direct replacement would require hardware modifications. Conversely, a microSD-to-SD adapter can provide compatibility, but the mechanical stability of the adapter in the target environment must be verified. 2. Interface Protocol and Signal Integrity - Both series support the SD 3.0 (UHS-I) protocol and share identical electrical characteristics. However, the PCB routing layout for microSD is more compact. - In high-speed data transfer applications, using a microSD card with an adapter may introduce impedance mismatch risks. Signal integrity testing under high-frequency or industrial vibration conditions is recommended. 3. Structural Reliability Differences - When an industrial-grade microSD card is used with an adapter, the increased number of connection points may reduce vibration resistance and mating cycle durability. - In embedded systems with high reliability requirements (e.g., transportation, industrial control), the long-term stability impact of the adapter solution should be assessed. It is advisable to prioritize models with native interfaces where possible.