The RTL9211DS is more commonly seen in storage bridges that enable M.2 NVMe SSDs to be used with a USB host. The Realtek card reader is a dual-chip solution that uses the RTL9211DS and RTS5261. The 250GB reference design sampled for review comes with the SanDisk / Kioxia BiCS 4 96L TLC 2-plane flash. The write performance is highly influenced by the number of flash pieces, NAND tPROG, and plane numbers. With 4 plane flash, Silicon Motion claims write performance of more than 700 MB/sec with four NAND flash pieces. Silicon Motion has qualified the SM2708 for operation with SanDisk / Kioxia 96L TLC (2-plane flash) and Micron B27B (96L) and B47R (176L) (both 4-plane flash). The controller is restricted to two-channel operation with 8 enables per channel, and both 3D TLC and QLC can be used. On the flash side, both Toggle 3.0 and ONFI 4.1 NAND interfaces at 800 MT/s are supported. The Silicon Motion SM2708 card controller supports both SD UHS-I and PCIe Gen 3.0 x2 on the upstream side. Silicon Motion coordinated with Realtek to sample their 250GB SM2708 reference design along with a card reader based on the the Realtek RTL9211DS and RTS5261 for this review. While SD Express cards are being enabled by controllers such as the SM2708, card readers platforms based on JMicron and Realtek have also appeared in various trade-shows (such as the RTS5261 demonstrated at Computex 2019). What We're Testing Today: SD 7.1 Reference DesignsĬonsumers need both SD Express cards and card readers in order to take advantage of all the benefits of PCIe / NVMe in the SD form-factor. That is about to change in the coming months, with both ADATA and Lexar announcing plans to launch their SD Express cards based on the Silicon Motion SM2708 card controller within the next few quarters. However, none went on to appear in the retail market. SD cards as well as card readers based on these new standards have been making the rounds at various trade shows since 2019. In order to serve the needs of all serviced markets, the SD Association introduced the NVMe-based SD Express standard (SD 7.0) in 2018, with a SD 8.0 follow-up in 2020.
SD cards are also popular in multiple market segments. CFexpress cards retain the XQD form-factor, and a few CFexpress cards are already in the market. In 2016, the CFA announced plans for the CFexpress standard and it was published in mid-2017. While the original CF cards were based on PATA (the precursor to SATA), a faster version based on SATA was introduced in 2009 as CFast. However, lack of backwards compatibility with existing CompactFlash readers meant that the format never really took off despite making its way into retail. The CFA had actually jumped on to PCIe quite early, with a 1Gbps standard in 2011 - the XQD card format.
Currently popular SD and CF cards are based on standards developed when SATA ruled the roost as the transfer protocol of choice for internal storage devices.Īs PCIe-based NVMe took the SSD storage market by storm, both the SDA and CFA introduced removable card standards based on PCIe.
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SD cards have also enjoyed support in the portable game console space and as boot drives for single-board computers.
SD cards and CompactFlash cards have emerged as the storage media of choice for content capture devices such as digital cameras and camcorders. It also serves as a preview of what consumers can expect from SD Express cards appearing in the market over the next few quarters. This review takes a detailed look at the performance of the card in conjunction with Realtek's RTL9211DS card reader reference design. Silicon Motion sampled us its SM2708 reference design (with a 250GB capacity) to put through our rigorous memory cards evaluation suite. The cards from both vendors are based on the Silicon Motion SM2708 controller. Both ADATA and Lexar have announced plans to launch their SD Express cards within the next few quarters.
Removable memory cards based on PCIe / NVMe are slowly starting to appear in the market - CFexpress from CFA, and SD Express from the SDA. The products currently servicing this market segment are based on technology standards drafted when SATA was the pinnacle of internal storage performance, but in fact both standards bodies jumped on to the NVMe bandwagon in the late 2010s. There are two main standards bodies in this segment - the SD Association (SDA) and the CompactFlash Association (CFA), with the SDA is responsible for the Secure Digital cards (SD / microSD), and the CFA has the CompactFlash and CFast card markets. Many computing systems (including PCs and smartphones) also employ them to augment the available storage capacity. Flash-based removable media, such as SD cards, have a host of use-cases in products ranging from content capture devices to portable game consoles.
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