There's been a change to MLC NAND

May 5, 2016 OpenSystems Media

Embedded OEM system designers should be aware of an MLC NAND memory transition that’s occurring in the market today. The handful of major NAND suppliers are rapidly moving production on the MLC NAND geometry from 19/20 nm to 15/16 nm.

At first glance, this seems like a positive event. Shrinking the trace width of memory components comes with lower cost, possibly higher performance or other attributes. These are all true items.

There are some other facts that should also be considered. Shrinking trace widths can change the endurance cycles per cell that the NAND is capable of performing prior to becoming unreliable. Typical endurance numbers for the transition from 19/20 to 15/16 nm show a drop from 3000 cycles per physical block to 2000 cycles.

With controller functions such as ECC, defect management, wear leveling, and other algorithms, the “logical” endurance in most applications can be increased substantially from the “raw” NAND endurance.

As with most flash storage changes, it’s important that embedded systems designers are aware of this phenomenon and have tested the new parts in any ongoing production systems. New memory, firmware, and/or silicon can introduce unforeseen issues to the host system design and cause latent defects to be shipped in field systems.

Most flash storage manufacturers don’t notify customers when there’s a firmware or other silicon change. They consider a 32-Gbyte SSD the same, regardless of what it looks like on the inside. While this is a manufacturing-friendly solution for the SSD OEM, it introduces inconsistent flash storage devices to the market—likely not an issue for end users with a client PC, but possibly a big issue for embedded systems.

To navigate this slippery slope, Cactus and a few other vendors offer locked-BOM, long-lifecycle flash storage devices, even on the MLC NAND based products. Product such as the MLC mSATA are available with this locked-BOM.

An embedded engineer can get a part with a certain BOM locked to a part number. When a transition occurs, like the one described here, engineers can get a new part number with the latest memory which can be tested and qualified in their application, prior to receiving it in the latest production shipment from their flash storage supplier.

Steve Larrivee is VP Sales & Marketing for Cactus Technologies and has over 30 years’ experience in the data storage market, including 10 years with SanDisk and 5 years at Seagate Technology.

Steve Larrivee, Cactus Technologies Limited
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