INTRODUCTION
To fully understand the types of NAND flash and how it works, it’s important to first understand the data we store in it and the amount of space this data occupies called a cell. Simply put, a cell in NAND flash means a reserved small space as a room, within the semiconductor, and the data can be any object that can occupy that reserved space of a room for the semiconductor, i.e the cell. In this case, storing data is like tiny object moving into these tiny rooms we call cells.
With this analogy, let us now study the different types of NAND flash. NAND flash is categorized into four different types plus one, depending on the data storage method employed. These are Single-level cells (SLCs), Multi-level cells (MLCs), Triple-level cells (TLCs), Quad-level cells (QLCs), and 3D V-NAND.
- Single-level cell:
Single-level cell (SLC) NAND, as the name indicates, stores one bit of data in each cell. There are two states SLC NAND can be in: programmed (0) or erased (1), which depends on the level of charge that is applied to the cell. Because the number of potential states in SLC is limited to two different values, determining the state of a cell is a quick process.
SLC NAND is the simplest of the NAND flash memory types, has a high speed attached with higher price, and has a very low chance of error. - Multi-level cell:
Perhaps the most cryptically named of the NAND flash types. Multi-level cell (MLC) NAND stores two bits of data per cell. This means that there are four possible states (00, 01, 10, 11,) as opposed to SLC's two. Serving as a midpoint between single- and triple-level cells. MLC are cheaper than SLC, but data processing speed is slow when compared to SLC. - Triple-level cell:
Boasting three bits per memory cell, triple-level cell (TLC) NAND is another type of NAND flash memory suited to consumer-level products. Also referred to as MLC-3, 3-bit MLC and X3. TLC NAND comes with a lower price tag than both SLC and MLC NANDs. There are eight possible states for TLC NAND: 000, 001, 010, 011, 100, 101, 110 and 111.
TLC has a higher storage density than SLC and MLC, lower cost per bit, and a slower speed than SLC and MLC. - Quad-level cell:
Quad-level cell (QLC) NAND stores four bits in each memory cell. Continuing with the previous trend, QLC NAND is cheaper than the above listed NANDs, but has lower endurance for writes. QLC was developed for the additional storage capacity it provides SSDs and is capable of faster reads than the other types of NAND flash.
QLC NAND is suited particularly to read-intensive applications and is used for applications supporting AI, machine learning and deep learning, where data is typically written once. In theory, QLCs are four times cheaper than SLCs because they divide one cell (which stores one bit of data) into four cells. So, if you’re looking for an ultra high-performance SSD, an SLC or MLC NAND flash SSD is the way to go. But if it’s economy you’re after, your best options will be TLC or QLC NAND flash SSDs. - 3D V-NAND:
While 2D or planar NAND has one layer of memory cells, 3D V-NAND stacks cells vertically in multiple layers. 3D V-NAND SSDs are formed by either combining MLC, TLC and QLC NAND technologies, but not SLC NAND. With 3D V-NAND architecture, an SSD has much higher density than with planar NAND, in a smaller physical space. Higher density means that 3D V-NAND SSDs are lower in cost per gigabyte, require less power consumption and have a higher write performance.
DIFFERENT INTERFACES THAT CAN BE FOUND WITH SSD
It’s also important to know the different interfaces SSDs used when it comes to how they are been connected to the host machine bus. It’s vital to understand exactly what distinguishes one from the other.
The three most common types of SSD storage interfaces, which are currently dominance in the marketplace, are SATA, SAS, and NVMe/PCIe.
- mSATA III, SATA III, and traditional SSDs SATA (Serial Advanced Technology Attachment):
SATA— sometimes called serial ATA—is a computer bus interface that was introduced back in 2000, making it the oldest of the SSD interfaces seen today. Its release represented a huge improvement over the Parallel ATA (PATA) interface that had been in use since the ’80s. Compared with its predecessor, SATA offered faster data transfer rates and less electromagnetic interference. It also enabled hot swapping—the ability to replace system components without needing to perform a system shutdown.
SATA is a half-duplex (one-directional) interface, so it cannot execute read and write functions simultaneously. This can result in serious performance delays, particularly in applications with heavy I/O processing demands. Nonetheless, SATA SSDs remain quite popular in the corporate world due to their relatively low cost. The latest SATA revision (3.5) was released in July 2020.
SSD SATA interface for connecting to host machine’s bus.
- SAS (Serial Attached SCSI)
SAS Small Computer System Interface, which hit the market in 2004, represents a significant technical advance over the earlier SATA interface. It deploys a point-to-point serial protocol that uses the SCSI (Small Computer System Interface) command set to transfer data to and from linked devices with a high speed and efficiency.
SAS can manage as many as 128 direct point-to-point connections, and its full-duplex capabilities enable simultaneous read and write functionality. SAS is also compatible with SATA devices, as its connections and backplanes are designed to accommodate SATA drives and protocols. This versatility has made SAS the preferred choice for many servers and workstations across the business world.
The latest SAS standard, SAS-4, arrived in 2017 and can support 22.5 Gbit/s transmission.![SAS and SATA SSD’s interface comparison]()
Comparison of SAS and SATA SSD’s interface
- PCIe and NVMe (Non-Volatile Memory Express) SSDs:
Introduced in 2011, NVMe was designed to address the shortcomings of the SATA and SAS interfaces, both of which were developed during the era dominated by the hard disk drive (HDD). The first interface to take full advantage of flash-based SSD tech, it uses a PCIe bus (Peripheral Component Interconnect Express) to communicate directly with the CPU, and dispenses with the host bus adapters (HBAs) that are required by SATA and SAS. Like SAS, it has full-duplex capabilities but far surpasses it in data transmission power.
By taking advantage of SSDs’ capacity for parallel computation and offering more channels, or lanes, for data transmission, NVMe sharply reduces latency and I/O overhead, which results in very high data transfer rates. It’s highly scalable as well - with bidirectional PCIe SSDs, you can get up to 32 lanes on one device. The most recent NVMe revision (2.0a) was released in July 2021.
Introduced a decade ago, NVMe has become a major player in the SSD world over the last few years. It is widely believed that NVMe will eventually supplant the older SATA and SAS interfaces. At the present time, though, it remains one of several viable options.![SSD interface for PCIe/NVMe]()
PCIe/NVMe SSD interface Manufactured by Acer Inc.
- Business:
Companies working with huge amounts of data (such as programming environments, data analysis companies, financial firms, telecommunication corporations, and streaming media, and video editing firms) often rely on SSDs, as access times and file-transfer speeds are critical. - Gaming:
Computers optimized for gaming have always pushed the limits of current technology, opting for more expensive equipment to boost gaming performance. That is particularly true for storage, as modern games constantly load and write files (textures, maps, levels, characters). New gaming consoles — like the PS5 and Xbox Series X — now used SSDs instead of hard disks. - Mobility:
SSDs have low power requirements, contributing to better battery life in laptops and tablets. SSDs are also shock resistant, which reduces the chances of data loss when mobile devices are dropped. - Servers:
Enterprise servers need SSDs to get fast read and write times to properly serve their client PCs.
APPLICATION AREAS FOR SOLID STATE DRIVES
SSDs were mainly used in those aspects of mission critical applications where the speed of the storage system needed to be as high as possible. Since flash memory has become a common component of SSDs, the falling prices and increased densities have made it more cost-effective for many other applications. Some of the application areas where SSD is beneficial are:
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CONCLUSION
The price of SSD keeps dropping each passing day to make it affordable to consumer. The introduction of SSD also gives computer and mobile phones manufacturers a room in creating devices that are smaller but with significant increase of performance and larger storage spaces on the device, which requires less power to function.
It is now a time to try upgrading your PC to SSD and experience the amazing features of this great storage device with your computer, if your computer has not come with SSD storage in it.
Read the previous articles on the series by visiting the folowing links:
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