SanDisk introduced its new iNAND 7232 storage solution for embedded applications, such as cellphones and tablets, at the Mobile World Congress in Shanghai, China. This new version of the embedded memory is an evolution from the previous iNAND 7132 that we covered in March.
SanDisk moved to 15nm 3bit-per-cell (TLC) NAND for this new implementation, which comes in capacities of 32 GB to 128 GB. The 15nm TLC NAND provides more density and lower cost for the underlying media. The new model features up to twice the capacity of the previous generation 7132.
The iNAND 7232 adheres to the eMMC 5.1+ HS400 specification, which also includes command queuing. The enhanced command queuing enables the device to process multiple commands in parallel, as opposed to resolving data requests in a serial fashion. The addition of command queuing also allows the eMMC products to remain competitive with UFS alternatives.
The increased speed is required for the higher resolution cameras and faster Internet connections, such as 802.11ac, in today's mobile devices. The iNAND offers sequential read speeds of 280 MBps and sequential write speeds up to 150 MBps in a tiny 11.5 x 13 x 0.9 mm package. For those keeping track, the 7232 has a 25 MBps faster sequential write speed, and it is the same size as the previous generation for width and length, but 0.1 mm thicker.
TLC doesn't have as much endurance or performance as MLC NAND, so SanDisk uses its second-generation SmartSLC technology. SmartSLC serves the dual purpose of increasing endurance and improving performance by catching all incoming write data in the more endurant SLC layer before passing it down to the TLC layer. This is becoming increasingly important as we move to smaller NAND lithographies, which inherently have less endurance.
According to the press release, SmartSLC boosts speeds up to 1.2 Gbps (gigabits), which is an improvement from the 1 Gbps boost of the previous generation. However, after a bit of conversion from Gbps to MBps we come out to the actual boosted speed being 150 MBps, which is not an increase over the normal rated sequential speed of the device. We reached out for comment from SanDisk, which indicated that the device can go beyond 1.2 Gbps, but it cannot specify any specific maximum speed.
SanDisk is also not releasing the random read/write performance metrics, instead focusing on the sequential performance specifications. The previous generation 7132 was listed at 3300/2800 read/write IOPS, and it is safe to assume the new version is slower in this aspect. The previous generation was also listed as offering 10 years of endurance, but there is no comparative data for the new model.
There are going to be unavoidable trade-offs in performance and endurance as manufacturers employ smaller 2D NAND designs, which is exactly why the move to 3D NAND receives so much attention. 3D increases the cell size, and thus provides more endurance and performance, which enables several more generations of NAND before we begin to encounter the same limitations.
The main driver of the smaller 2D planar NAND lithographies is to provide a more cost-effective price point. The iNAND 7232 is sampling now to customers.
An interesting side note: SanDisk also announced it has produced over two billion microSD cards since it began shipping them 10 years ago. These two billion cards equal an estimated capacity of 11,103 billion megabytes, or enough flash to give every man, woman and child who has ever lived on earth 100 MB of storage.
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