The XFMExpress standard is ready, the first products should be on the market soon: Kioxia has the first corresponding cards, which are hardly larger than micro SD cards with dimensions of 18 mm × 14 mm × 1.4 mm. But the speed increases significantly with two PCI Express 4.0 lanes – XFMExpress cards are practically SSDs in a mini form factor.
With the two PCIe 4.0 lanes, sequential transfer rates of almost up to 4 GB/s are possible. the According to Kioxia, the card size is chosen exactly the same waythat a NAND flash device fits in. In the first generation, Kioxia is launching its XFMExpress SSDs with capacities of 256 and 512 GB. 1 TB models will follow later.
Kioxia already showed the first XFMExpress prototypes in the summer of 2019 – at that time still with PCIe 3.0 x1 (max. 1 GB/s) – and submitted the design to JEDEC for manufacturer-independent specification. The latter released version 1.0 under the name XFM Device in August 2021. Kioxia is currently supplying partners who are testing the mini-SSDs for inexpensive notebooks, for example.
eMMC replacement for notebooks
XFMExpress SSDs are primarily intended to replace soldered eMMC data carriers in cheap notebooks and embedded systems and also soldered BGA SSDs. They use a card slot reminiscent of micro SD or SIM slots. Compared to eMMC storage, XFMExpress cards would not only be faster, they would also greatly increase the ability to repair and upgrade.
Diagram from Kioxia’s (then Toshiba) presentation in 2019: The size has remained the same since then, only the arrangement of the pin rows has changed.
(Image: Kioxia)
Unlike high-end SSDs in the M.2 format, XFMExpress models do not have a DRAM cache. However, the NVMe protocol used can potentially help here: It can use the system’s main memory as a buffer to speed up access.
Despite its speed, XFMExpress has no future, at least in high-end cameras. For these there are SD Express cards that jump on the PCIe and NVMe train, but are still backwards compatible with the oldest SD standards. However, development is progressing slowly: The specification SD Express 7.0 with only one PCIe 3.0 lane (max. 1 GB/s) dates from 2017 – only now are the first cards on the market. The SD Association passed version 8.0 with two PCIe 4.0 lanes in May 2020.
(mma)