We have seen an increase in the number of new mainstream SSDs lately. This has been made possible by Micron’s new 128Gbit NAND, which has helped to bring costs down, making them more attractive to users who only require an SSD for mainstream, everyday computing purposes.
For many users, 256GB (or 240GB) is the magic sweet spot capacity point for SSDs. There are two main reasons for this: one, it is at a more palatable price point for a reasonable sized capacity; and two, NAND parallelism ensures that at 256GB, there are enough NAND dies to go around to maximize the performance of the memory controller. To understand NAND parallelism, we need to know that one of the reasons why SSDs are so much faster than traditional hard disk drives is that apart from the fact that there are no moving parts, SSDs can read and write to multiple NAND dies almost simultaneously. Understanding this, we can see that as long as the memory controller is capable, having additional NAND dies usually translates to better performance.
However, one of the problems of using high density memory packages for 256GB capacity SSDs is that when you double the capacity of the die, it also means that you need lesser dies to make up the required 256GB capacity. As a result, there would not be enough NAND dies to maximize the performance potential of the memory controller, leading to a performance degradation. And this was exactly what happened to the Crucial M500.
To rectify this, Crucial introduced the new M550. For the M550, Crucial has reverted to 64Gbit NAND for its 128GB and 256GB drives to improve performance, while its 512GB and 1TB models continue to use 128Gbit NAND - the sheer capacity of the larger capacity drives necessitates more dies and thus saturates the channels of the memory controller.
In addition, the new Crucial M550 also has the updated Marvell 88SS9189 controller, which is an incremental update over the older 88SS9187, adding support for LPDDR and improved DevSleep optimization, both of which are power-saving features.
Another new mainstream SSD to hit the market recently is ADATA’s Premier Pro SP920SS (which will be referred to simply as the SP920SS from here on). The name ADATA might not ring any bells, but Taiwanese-based ADATA is one of the world’s largest manufacturers of DRAM modules and have recently added SSDs in their product portfolio. In fact, we reviewed ADATA’s previous flagship - the XPG SX900 - in our inaugural Great High-end SSD Shootout.
Like the Crucial M550, the ADATA SP920SS is also equipped with Marvell’s new 88SS9189, and it is also one of the first brands outside of Crucial to use Micron’s new 128Gbit NAND. Upon further investigation, we also noticed that the ADATA SP920SS’ firmware has the exact same codename as the Crucial M550 - MU1. In light of this, we have every reason to believe that the ADATA SP920SS is in fact a rebranded M550.
However, unlike the M550, the SP920SS series will use Micron’s new 128Gbit NAND across all models, and this would result in lower performance for the lower capacity 128GB and 256GB drives. As explained earlier, higher density NAND reduces the number of NAND dies used, which in turns reduces performance as as a result of decreased NAND parallelism. How this will impact performance will be interesting to see.