What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Verdict: Silicon Motion’s SM2708 proves that an SD Express card can behave like a small, removable NVMe device. AnandTech’s 250GB reference card reached about 890 MB/s reads and 418 MB/s writes—roughly SATA-SSD territory—but sustained writes fell below 100 MB/s after its approximately 5.5GB SLC cache filled, while the card reached about 99–100°C in testing. It is an impressive technology demonstration, not a universal replacement for CFexpress or a properly cooled internal SSD.
The practical question is compatibility. SM2708 provides PCIe Gen3 x2 and NVMe operation only when the host and reader expose SD Express mode. In an older camera, laptop, console or USB reader, the same card can fall back to ordinary UHS-I speeds.
| # | Preview | Product | Price | |
|---|---|---|---|---|
| 1 |
|
Samsung microSD Express Card – 256GB for Nintendo Switch™ 2 | $59.00 | Buy on Amazon |
| 2 |
|
SANDISK 512GB microSD Express Card | $129.99 | Buy on Amazon |
| 3 |
|
Samsung P9 Express microSDXC Express Memory Card 256GB | $79.25 | Buy on Amazon |
| 4 |
|
SANDISK 256GB microSD Express Card | $58.99 | Buy on Amazon |
| 5 |
|
Lexar 512GB Play PRO Micro SD Express Card, 900MB/s Read, 4K, V30, UHS-I | $126.80 | Buy on Amazon |
What SM2708 and SD Express actually are
SM2708 is Silicon Motion’s controller; SD Express is the card standard and its PCIe/NVMe interface; the reviewed unit was a complete 250GB reference design with NAND and firmware; and the Realtek RTL9211DS was the reader used to expose PCIe mode. Those are different parts of the system, so controller specifications do not determine every retail card’s capacity, temperature, cache or warranty.
Ordinary UHS-I cards communicate over the legacy SD bus. SD Express adds PCIe and NVMe lanes while retaining UHS-I backward compatibility. Silicon Motion’s product brief lists PCIe Gen3 x2, NVMe 1.3, UHS-I modes including SDR104, and theoretical throughput of up to 900 MB/s in SD 7.0/7.1 PCIe Gen3 x1 mode or 1,700 MB/s in SD 8.0 PCIe Gen3 x2 mode (product brief). Silicon Motion’s later corporate material describes NVMe 1.4, so the NVMe version depends on which documentation and firmware generation is being discussed.
#1 Best Overall
- Nintendo Switch 2 uses a new standard of expandable memory card called microSD Express (sold separately). This kind of memory card is needed for faster access speeds and to ensure games will run smoothly.
- Please note: Nintendo Switch 2 is only compatible with microSD Express cards. If the microSD cards you have used for Nintendo Switch do not support microSD Express standards, you cannot use them with Nintendo Switch 2.
The 1,700 MB/s figure is an interface/controller ceiling, not a guaranteed card result. The SM2708 has two NAND channels, and the reference card used two NAND packages. Package count, die and plane configuration, firmware, NAND type, cache policy and cooling all affect the finished product.
How the reference card was tested
AnandTech tested the 250GB reference card in a Quartz Canyon NUC with the RTL9211DS reference reader, exFAT formatting, CrystalDiskMark, fio, PCMark 10 and repeated file-transfer workloads. The review compared fresh and extended-use states and examined sustained transfers rather than relying only on short benchmarks. Its documented Windows copy command was robocopy /NP /MIR /NFL /J /NDL /MT:32 <source> <destination>; that is historical test methodology, not a requirement for normal use (test details).
Specifications versus measured performance
| Item | Result or specification | Qualification |
|---|---|---|
| SD Express interface | PCIe Gen3 x2 | SD 8.0 mode; controller specification |
| Theoretical throughput | Up to 1,700 MB/s | Silicon Motion maximum claim, not a card guarantee |
| Fresh sequential read | Approximately 890 MB/s | AnandTech’s 250GB reference sample |
| Fresh sequential write | Approximately 418 MB/s | Same sample and benchmark |
| SLC cache | Approximately 5.5 GB | Observed behavior of the reference card |
| Post-cache writes | Below 100 MB/s in parts of testing | Workload- and state-dependent |
| Peak temperature | Approximately 99–100°C | Observed in AnandTech’s test setup, not universal |
Sources: Silicon Motion and AnandTech.
Burst performance is genuinely SSD-like
Fresh CrystalDiskMark results of roughly 890 MB/s reads and 418 MB/s writes put the reference card well beyond UHS-I and near SATA-SSD sequential performance. PCMark 10 showed similarly encouraging behavior: SD Express was broadly comparable to a high-end SATA SSD in boot-oriented, read-heavy work, tracked 256GB-class SATA or DRAM-less SSDs in some creative tasks, and delivered SATA-like results in mixed file-transfer workloads. That is a remarkable result for removable media, but it is not equivalent to a modern high-end NVMe SSD across every workload.
Rank #2
- NEXT GEN GAMING: Works with Nintendo Switch 2.
- READY FOR TOMORROW. Ready for future products with a PCIe-NVMe interface; performs at UHS-I speeds with microSD UHS-I and UHS-II devices.
- EXPONENTIALLY FASTER PERFORMANCE. Up to 4.4 times faster transfer speeds than our fastest microSD UHS-I cards [9]. Transfer a 2-hour HD movie in less than 3.5 seconds [1]; save up to 2.8 minutes transferring 60 minutes of 4K UHD video [4] shot at 30 fps when paired with the SanDisk PRO-READER SD Express Dual Card (sold separately) [9]
- DURABILITY YOU CAN COUNT ON: Cards are waterproof, temperature-proof, humidity-proof, drop-proof, shock-proof, magnetic-proof, x-ray proof, and wear-out proof [5].
- HEAT MANAGEMENT REIMAGINED. SanDisk ThermAdapt helps keep devices from overheating with a specially designed enclosure and controller that uses dynamic adaptive thermal management.
Reads stayed strong during large-file testing, often exceeding 500 MB/s. This makes the technology particularly attractive for offloading large media files, loading game data and other read-heavy tasks where the host can sustain PCIe operation.
Quick wins for a faster PC:
Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Sustained writes expose the cache limit
The card uses pseudo-SLC caching: incoming data is first absorbed by faster SLC-mode NAND, then folded into native TLC storage. Short benchmarks can fit mostly inside that cache and produce headline numbers. Once the approximately 5.5GB cache was exhausted, large-transfer writes dropped below 100 MB/s in portions of AnandTech’s testing (sustained testing).
That distinction matters for continuous video capture, game installation, disk imaging and large backups. A card can feel instant for a burst and then behave like a much slower flash device during the rest of a long transfer. NAND parallelism also limited the sample: Silicon Motion supports two channels, and reporting around the launch indicated that four-plane NAND was expected to improve writes on other configurations (The SSD Review).
Rank #3
- TRANSFER SPEEDS UP TO 800 MB/S: With sequential read speeds up to 800 MB/s, get into your game up to 4× faster than our standard microSD cards (UHS I)¹.
- DYNAMIC THERMAL GUARD: Keeps its cool even when the action heats up. Dynamic Thermal Guard helps reduce overheating for fast, smooth gameplay.
- ALL YOUR GAMES ON ONE TINY CARD: Store all your games and downloadable content (DLCs) with up to 512GB of reliable storage. No deleting. No compromises.
- 6-PROOF PROTECTION WITH 3-YEAR LIMITED WARRANTY: Built to last, made for peace of mind. Anything can happen when you’re gaming on the go. With 6 types of protection²⁻⁹, the P9 Express can handle it all—helping maintain your game progress.
- NEXT-GEN AND BACKWARD COMPATIBLE: Your microSD Express card is compatible with Nintendo Switch 2¹⁰ and microSD UHS-I¹¹ devices, including tablets, drones, cameras and more.
Heat is the “served hot” problem
AnandTech measured approximately 99–100°C during extended workloads on the reference design. PCIe/NVMe operation consumes more power than legacy UHS-I, while an SD card has little surface area for heat dissipation. Firmware throttling or speed caps may therefore appear only after a sustained transfer. A sealed camera body, handheld console or enclosed reader can be more difficult thermally than the open test setup.
The temperature is specific to that card, reader, firmware, airflow and workload. It should not be treated as a universal SM2708 operating temperature. Any serious evaluation should log temperature during a full-capacity write, not just run a short peak-speed test.
Recommended Free Tools
Used-state performance and the unusual format recovery
After extended use, the reference card’s approximate results fell from 890 to 733 MB/s reads and from 418 to 95 MB/s writes. Formatting it in SD Express/NVMe mode restored about 878 MB/s reads and 415 MB/s writes. AnandTech found that formatting in UHS-I mode did not provide the same recovery (performance-restoration results).
Rank #4
- NEXT GEN GAMING: Works with Nintendo Switch 2.
- READY FOR TOMORROW. Ready for future products with a PCIe-NVMe interface; performs at UHS-I speeds with microSD UHS-I and UHS-II devices.
- EXPONENTIALLY FASTER PERFORMANCE. Up to 4.4 times faster transfer speeds than our fastest microSD UHS-I cards [9]. Transfer a 2-hour HD movie in less than 3.5 seconds [1]; save up to 2.8 minutes transferring 60 minutes of 4K UHD video [4] shot at 30 fps when paired with the SanDisk PRO-READER SD Express Dual Card (sold separately) [9]
- DURABILITY YOU CAN COUNT ON: Cards are waterproof, temperature-proof, humidity-proof, drop-proof, shock-proof, magnetic-proof, x-ray proof, and wear-out proof [5].
- HEAT MANAGEMENT REIMAGINED. SanDisk ThermAdapt helps keep devices from overheating with a specially designed enclosure and controller that uses dynamic adaptive thermal management.
This is behavior observed on the reference sample, not a universal maintenance rule. Deleting files is not necessarily equivalent to restoring the controller’s internal free-block state, and reformatting destroys data, so it is a troubleshooting step only after a verified backup.
Compatibility checklist before buying
- Confirm the host: the camera, console, laptop or single-board computer must explicitly support SD Express PCIe/NVMe mode.
- Confirm the reader: a conventional USB SD reader may expose only UHS-I. The reader bridge, firmware and USB link can all be bottlenecks.
- Check the operating system: in SD Express mode the card may appear as an NVMe device; platform firmware must support that path if you intend to boot from it.
- Test the actual device: physical fit and backward compatibility do not prove PCIe operation. Benchmark in the target host.
- Check sustained results: require multi-gigabyte or full-capacity writes, temperature data and fresh-versus-used measurements for the exact capacity.
- Verify endurance and warranty: SM2708’s ECC and data-path features do not establish a universal TBW rating. Use the finished card vendor’s terms.
Where it fits—and where it does not
Cameras and video
SD Express can shorten offload and ingest for RAW and high-resolution video, while keeping a familiar SD shape. Recording is more demanding: the camera must certify SD Express, the write rate must remain high after cache exhaustion, and heat inside the body must be acceptable. Sequential burst results alone are not evidence of reliable long-duration recording.
Portable gaming
On a compatible handheld, faster reads can improve installation and loading, and microSD Express can provide the same idea in a smaller package. Device firmware, enclosure temperature, capacity layout and price determine whether the benefit is real. A UHS-I-only system gains none of the PCIe speed.
Best Value
- The perfect card for the Nintendo Switch 2 delivers revolutionary performance that is 4x faster than typical UHS-I microSD cards
- PCIe technology delivers read speeds up to 900MB/s so the game loads faster
- Write speed up to 600MB/s deliver accelerated download speeds when paired with the Lexar microSD Express card reader
- Level-up your handheld gaming experience with next-gen tech
- 1TB microSD Express card offers more space for your favorite games
PC removable storage
An SD Express card can serve as removable scratch or secondary storage and may appear as NVMe. It remains removable flash with limited cooling and potentially weaker sustained writes and endurance than an internal SSD, so it is a poor choice for heavy scratch workloads or large recurring backups.
SM2708 compared with the alternatives
| Option | Strength | Limitation |
|---|---|---|
| UHS-I SD | Broadest compatibility and simpler thermals | Much slower |
| UHS-II SD | Faster camera workflow where supported | Requires UHS-II host and reader; different interface |
| CFexpress | Often stronger sustained performance for professional capture | Dedicated hardware, larger formats and potentially higher cost |
| USB NVMe SSD | Better cooling, capacity and long-transfer consistency | Cable or enclosure; less integrated than a card |
| Internal M.2 NVMe SSD | Best performance, endurance and capacity | Not removable in the SD-card sense |
| microSD Express | Small form factor for supported handhelds | Even tighter thermal and compatibility constraints |
Market status and buying judgment
The original review was published on September 9, 2021 and covered a reference design, not a retail model with a consumer warranty or standardized NAND. In a 2026 corporate blog, Silicon Motion says SM2708 products have been adopted by Samsung, ADATA, Lexar and Biwin, including Samsung’s P9 Express microSD card for Nintendo Switch 2 (Silicon Motion’s ecosystem announcement). That is a manufacturer claim about adoption, not independent proof of universal compatibility, availability or equal performance.
Choose an SM2708-based card only when the host and reader explicitly support SD Express, the workload benefits from fast reads or short bursts, ventilation is adequate, and exact-card sustained-write, thermal, endurance and warranty information is available. Prefer UHS-I for maximum compatibility, UHS-II for a supported camera workflow, CFexpress for proven professional sustained recording, or USB/internal NVMe when cooling and long-transfer consistency matter more than SD-card convenience.
Final verdict
SM2708 demonstrates that an SD card can become a removable NVMe device: the reference design delivered SATA-SSD-class reads and impressive mixed-workload behavior. Its weaknesses are equally important—cache-dependent writes, roughly 99–100°C observed temperatures, limited parallelism, variable retail implementations and strict host/reader requirements. Treat it as a promising SD Express platform, not as a miniature high-end M.2 SSD or a direct CFexpress replacement.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
