The ability to hot swap storage media from servers or consumer electronics is taken for granted. A new standard is aimed making it easier to change out flash memory that’s typically been soldered into connected devices and embedded applications.
The JEDEC Solid State Technology Association has released its first iteration of the Crossover Flash Memory (XFM) Embedded and Removable Memory Device (XFMD) standard. The spec outlines a new universal data storage media providing an interface between NVM Express (NVMe) and PCI Express (PCIe) in a small, thin form factor.
As it becomes commonplace to switch out SSDs from servers rather than replacing an entire rack, XFMD is designed as a replaceable storage medium for devices that are typically soldered and meant to stay put for the lifespan of the device in which they are embedded.
Bruno Trematore, who helps oversee JEDEC’s JC-64 committee on embedded memory storage and removable memory cards, said XFMD serves as a “crossover” between an embedded memory and memory cards such as SD card or compact flash. Examples include gaming consoles, virtual and augment reality gear, video recording devices such as drones and surveillance systems, even automotive applications where components are typically qualified to last a decade.
The XFMD measures 13 mm by 18 mm and 1.4 mm high, Trematore said, making it smaller than a standard SD card but still larger than a microSD card. “It’s so small that you can compare it in size with a soldered memory like UFS,” or universal flash storage. “It’s still thick enough to stack memory inside. Although XFMD isn’t hot-swappable, it’s much easier to exchange than many of the embedded flash memories such as UFS and eMMC, which are often used in automotive applications.
XFDM uses PCIe and NVMe for connectivity—the PCIe interface provides fundamental bus connectivity while NVMe serves as the higher-level protocol for accessing non-volatile media as a low-latency logical storage device. Trematore said NVMe is one of the most widespread protocols, “so this allows connectivity with a majority of systems out there on the market.”
Although PCIe and NVMe are widely used in data centers, XFMD is unlikely to be added to enterprise servers.
Rather, the spec targets Internet of Things devices expected to last at least a decade but need storage expansion as data grows exponentially and capacity requirements exceed original design specifications. “We see a gap in the market” that could be filled by XFDM, said Trematore.
Other uses include as a buffer for video recording or in dash cams and other ADAS devices that are continuously being overwritten, leading to the flash storage wearing out before a car—essentially anywhere where more data is written than anticipated. “You’re just replacing a part,” he added.
Underestimating how many writes a flash device might need in automotive applications is far from theoretical. In early 2021, Tesla issued a recall due to NAND flash wearing out in an embedded multimedia card.
Although automotive applications are well suited for XFMD, the standard doesn’t address temperature ranges, said Trematore. That consideration falls to device makers implementing the spec. While flash memory is unaffected by cold temperatures, excessive heat is a consideration.
XFMD has been under development for a year. The short timeframe suggests there’s a great deal of industry interest, in part due to the standard’s flexibility. Still, significant adoption will be required before commercial products hit the market.