Many companies were surprised by the unexpected eMMC developments last November, when Samsung announced availability of a 260MB/s eMMC device. The announcement roiled the mobile storage industry and led JEDEC
to hastily finalize a revision to the eMMC specification. The result is eMMC 5.0 with a peak transfer rate of 400 MB/s (equivalent to 3.2 Gbps). This moves eMMC slightly ahead of UFS v1.1 with 2.9 Gbps transfer rate. To further blur the advantage of UFS, some advanced features originally intended for UFS are now been planned for future eMMC revisions.The new eMMC 5.0 specification will also be introduced in the 3rd quarter of this year; its maximum data transfer rate will be 400MB/s or 3.2 Gbps in 8-bit bus operation. This high data transfer rate fills the performance gap before UFS entire ecosystem is available. In addition, an eMMC version of command queuing is now on eMMC roadmap for a future specification revision. It is also possible that eMMC will continue to increase the maximum data transfer by another factor of two.
Is UFS adoption in tablets and smart phones threatened by the recent advent of eMMC 5.0?
UFS version 2.0 will be introduced in the 3rd quarter of this year; its maximum data transfer rate can be 11.6 Gbps in a two-lane configuration with 5.8 Gbps per lane. In addition, native command queuing, inherited from the high performance SCSI protocol has been added. This provides multi-thread or multi-tasking operations which can provide an order of magnitude performance advantage over eMMC. A special extension has been added for Uniform Memory Access (UMA). This feature will allow non-volatile memory devices to extend on-die buffer storage for L2P (logical to physical) mapping. This can improve performance and device lifetime.
It seems like eMMC is positioned to fill the performance gap before UFS ecosystem (HW, SW, OS support, development tools, etc.) is ready. As a new technology, UFS will initially be adopted by high-end mobile devices. As the benefits of UFS are fully demonstrated in initial products, and the technology matures with increasing volume, UFS adoption will spread. UFS is supported by UFSA, a governing body of industry representatives chartered to define and certify compliance to the UFS standard.
UFS relies on the MIPI M-PHY. The M-PHY V2.0 supports transfers of up to 5.8Gbps (Gear 3) and is being adopted by additional standards bodies, e.g PCISIG for mobile PCIe, and USB for SSIC. This will further lower barriers to UFS adoption in high bandwidth, power critical applications.
Written by Sam Beal