The XFM standard is intended to combine the advantages of M.2 SSDs and BGA SSDs. Kioxia is now launching the flash memory form factor, reminiscent of a memory card, for compact mobile computers, IoT devices and embedded applications.
The new Cross-Over-Flash Memory (XFM)
The abbreviation XFM stands for Cross (X) Over Flash Memory and was chosen as the official memory standard with the specification JEDEC XFM Device 1.0 last year. The driving force behind this is the JEDEC member Kioxia, which around three years ago, at that time still under the name Toshiba Memory, described a new form factor for small flash memory modules including a suitable slot under the brand name XFMExpress.
At first glance, the 14 × 18 × 1.4 mm (L×W×H) memory module with an area of 252 mm² is reminiscent of a microSD memory card, which is even more compact at 11 × 15 × 1.0 mm (L×W×H). The height of 1.4 mm corresponds to the miniSD form factor. The mini memory can hide behind a 1 euro coin.
XFMExress (Image: Kioxia) Rather, XFMExpress is a new SSD form factor for single-package models. So far, Kioxia has served this area with SSDs such as the BG4 series, which measures 22 × 30 mm (L×W) as a pluggable M.2 SSD or in a BGA package measuring 16 × 20 mm (L×W) directly on the motherboard is soldered. XFMExpress aims to combine the compactness of BGA with the flexibility of M.2. The modular design with base (2.2 mm high) offers the advantages of upgradeability and repairability, which collects plus points in sustainability.
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XFMExpress: memory module and socket (Image: Toshiba Memory)
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XFMExpress: memory module and socket 
A maximum of 4 GB/s (PCIe 3) or 8 GB/s (PCIe 4) gross is possible 
The XFMExpress socket is from JAE 
Compactness of BGA SSDs and interchangeability of M.2 SSDs combined 
Compact package for slim mobile devices 
XFMExpress supports PCIe 3/4 with up to 4 lanes 
XFMExpress as a new form factor for flash memory PCI Express is used as the electrical interface, with one, two or (optionally) four lines (lanes) of the PCIe 3.0 and PCIe 4.0 standards being supported. This results in gross data rates of almost 1 GB/s (1 lane), 2 GB/s (2 lanes) and 4 GB/s (4 lanes) via PCIe 3.0 or twice the data rate with PCIe 4.0. In the future, PCIe 5.0 will be supported with data rates being doubled again.
The first products
Unsurprisingly, Kioxia is also making the first products based on the XFM standard. The Kioxia XFMExpress XT2 series includes 256GB and 512GB memory; previously up to 1 TB had been promised. The removable storage uses PCIe 4.0 x2 for just under 4 GB/s gross. The net data rate should reach a maximum of 3.5 GB/s, but ultimately depends on the NAND flash and controller used. However, there is no information about the latter components yet.
The main features of XFMExpress XT2 describes Kioxia as follows:
- High maintainability– The XFMEXPRESS XT2 enables a new category of small storage devices that are easy to maintain and expand. Combining a rugged, compact body, removable storage functionality and flexibility, the XFMEXPRESS XT2 helps break down technical barriers and design constraints.
- Ideal for mobile devices– The JEDEC XFM DEVICE 1.0 form factor, with its small size and low profile (14mm x 18mm x 1.4mm), occupies only 252 square millimeters [2] of space, optimizing the space required when built into ultra-compact host devices without sacrificing performance or serviceability. Thanks to the minimized device height of just 1.4 millimeters, the XFMEXPRESS XT2 is ideal for slim and light notebooks and creates new design possibilities for next-generation applications and systems.
- Interface – The XFMEXPRESS XT2 is designed for speed and includes an interface with PCIe 4.0 x 2 lanes and NVMe 1.4b. The storage device's industry-leading [3] performance and robust form factor offer a compelling alternative to other SSD form factors (such as M.2) and enable premium computing and entertainment experiences.
< p class="p text-width">Kioxia wants to demonstrate the XFMExpress XT2 at the Embedded World 2022 trade fair in Nuremberg (June 21-23) and at the Flash Memory Summit (August 2-4) in California. The press release is already talking about the market launch. However, concrete end products that use the new standard are not listed.