- What is pseudo SLC (pSLC) NAND?
- How pSLC fits in embedded applications.
- Cost and reliability tradeoffs of using pSLC.
以其高性能，可靠性，紧凑的外形，低功耗和在延长温度范围内工作的能力而闻名，单层电池（SLC）NAND作为基石NAND NAND FLASH技术分开。鉴于其多个积极属性，SLC NAND在各种物联网（IoT），汽车和新兴的嵌入式应用程序以及其他需要长寿和/或高可靠性的应用程序中找到了受欢迎的家也就不足为奇了。
SLC NAND在成本和性能之间提供了理想的平衡，用于存储启动和小型OS代码用于许多应用（见图）。Yet, for high-density storage applications, it presents a major drawback: cost. In fact, the technology can often be prohibitively expensive.
属性和特征
直到最近，设计师面临严重的困境。人们可以采取谨慎的态度，转向耐用但昂贵的SLC NAND，或者选择较低的成本，但性能较低，性能较慢，多级别电池（MLC）（MLC）和三级电池（TLC）NAND。但是，今天，有一个更好的选择：伪SLC（PSLC）NAND技术。
With pSLC NAND, the likes of MLC NAND, TLC NAND, and quad-level-cell (QLC) NAND can be used in an approach that lowers the number of bits stored in each cell to just one. It's important to note that MLC NAND natively stores two bits per cell, TLC NAND stores three bits per cell, and QLC NAND accommodates four bits per cell. Reducing the number of stored bits in each cell to only one increases the NAND's lifespan and reliability while lowering cost—a win-win proposition.
PSLC NAND以类似于SLC NAND的方式运行，但程序擦除周期较少，这使其成为SLC NAND的经济高效替代品。从使用最新的3D技术的角度来看，PSLC也很有吸引力。
Although pSLC NAND technology shrinks MLC NAND memory capacity by 50%, TLC capacity by 66.6%, and QLC NAND capacity by 75%, it still manages to deliver a significantly lower cost-per-bit than ordinary SLC NAND thanks to its higher cell density. Furthermore, pSLC NAND boosts reliability, performance, and endurance attributes to levels closely comparable to costlier SLC NAND technology. For most industrial applications, though, pure SLC NAND devices still provide the best reliability. Besides its rapid read speed, pSLC NAND also offers up to 10X greater endurance than TLC NAND.1
不利的一面是，PSLC NAND设备与MLC NAND对应物（即小单元）具有不利的特征（与其他NAND技术相比）。这意味着PSLC NAND更容易出现腐败，细胞串扰，读取干扰错误和保留数据问题。此外，由于PSLC NAND限制了每个单元格的数据存储，因此它没有标准（但价格更高又更具成本的SLC NAND提供的设备架构优势。
When all of the price, implementation, and performance factors are considered and evaluated, it becomes clear that pSLC NAND technology provides both a long-term service life and great cost value. Although pSLC NAND adopters should realize that they’re not going to obtain the same high reliability levels provided by pure SLC NAND, the newer technology's lower cost, yet still generally high reliability characteristics, make it an optimal choice for a wide range of storage applications.
Cost Considerations
较低的成本通常是转向PSLC NAND的主要原因。尽管PSLC NAND采用者永远不会实现纯SLC NAND的高可靠性，但价格可靠性/平衡或权衡总是会发挥作用。
在考虑使用新的存储技术时，SLC NAND通常会赢得这场比赛。另一方面，如果项目的主要目标只是仅仅实现每千兆字节的纯粹成本，并且最大化总体存储容量，可靠性和耐用性都是相对不重要的，那么TLC仍然是最低价格的选项。
用例
Today's NAND market is primarily driven by the growing demands of data-center technology providers, smartphone manufacturers, and other high-density device customers. Such buyers seek high-density NAND solutions that can provide storage at the lowest possible cost per gigabyte. On the other hand, for developers focusing on lower-density applications that require a NAND with strong reliability and endurance characteristics, the only realistic options are either pSLC NAND or costlier SLC NAND.
对于SSD应用程序，它们通常使用PSLC分区的组合以及MLC/TLC模式。PSLC NAND提供了一种解决方案，该解决方案大于其他人的存储应用程序，这些应用程序需要高可靠性，耐用性以及完全维护和保护代码和数据完整性的能力。
Overall, pSLC NAND is a good fit for applications that require SLC NAND-level endurance but can't tolerate the high-cost burden associated with pure SLC NAND. In the battle between flash attributes and cost, pSLC NAND offers a better compromise of reliability, speed, and endurance when compared to pure SLC NAND, with only a few modest drawbacks. Remember, too, that high-density SLC NAND is becoming increasingly hard to find, a challenge that designers must consider when selecting an appropriate NAND technology.
Specific pSLC NAND applications include high-endurance SD cards (cards used by surveillance cameras, for example), network cards, and small SSDs. In fact, any application that must reliably function in an environment with extreme high or low temperatures can benefit from pSLC NAND technology.
Particularly effective areas for pSLC NAND technology include devices and systems that routinely experience extreme environmental conditions, such as in cell tower equipment, outdoor signage, industrial sites, outside IoT devices, and even space vehicles and satellites. pSLC partitioned NAND is also well-suited for use in automobiles, trucks, trailers, motorcycles, and scooters, as well as all types of aircraft and seagoing vessels—any type of moving vehicle that's likely to experience extreme internal and external temperature conditions.
结论
重要的是要记住，尽管PSLC NAND作为突破性存储技术已经到达，但它永远不会完全消除对纯SLC NAND设备的需求。应用，性能和可靠性要求将始终作为基准，最终确定应使用哪种SLC NAND解决方案。
Brian Kumagai是记忆业务部门的主任美国的美国公司
