The type of NAND you choose for your SSD makes all the difference when it comes to performance, but sometimes, SSD manufacturers will have party tricks to help you boost your performance. One of those party tricks is SLC cache. And it actually does make a difference.
What’s SLC caching?
Like a high-speed buffer inside modern drives
You will often see blazing fast read and write speeds plastered across spec sheets and packaging for SSDs. But the physical memory chips inside the drive are likely not natively capable of sustaining those maximum speeds indefinitely. This is where SLC cache comes in. Most consumer drives on the market today use triple-level cell or quad-level cell memory, which stores three or four bits of data per memory cell, respectively. Storing multiple bits per cell drastically reduces manufacturing costs and increases storage capacity, making large drives affordable for everyday users. But the trade-off is that writing multiple bits into a single microscopic cell is a complex, relatively slow process requiring precise voltage adjustments.
Quiz
SSDs, NAND memory, and interfaces
Trivia challenge
From flash cells to PCIe lanes — see how much you really know about modern solid-state storage.
NANDInterfacesHardwarePerformanceStandards
Which type of NAND flash stores exactly one bit of data per cell?
Correct! SLC stands for Single-Level Cell, meaning each cell holds just one bit — either a 0 or a 1. This makes SLC the fastest and most durable NAND type, but also the most expensive per gigabyte, so it’s mainly found in enterprise and industrial storage.
Not quite — the answer is SLC, which stands for Single-Level Cell. MLC stores 2 bits, TLC stores 3, and QLC stores 4 bits per cell. The more bits per cell, the cheaper but slower and less durable the NAND becomes.
What does NVMe stand for in the context of SSDs?
Correct! NVMe stands for Non-Volatile Memory Express, a communication protocol designed specifically for flash-based storage. Unlike AHCI, which was built for spinning hard drives, NVMe takes full advantage of PCIe’s parallel lanes to deliver dramatically lower latency and higher throughput.
Not quite — NVMe stands for Non-Volatile Memory Express. It’s a host controller interface protocol designed to replace the older AHCI standard, which was originally built with spinning hard disk drives in mind rather than fast flash storage.
Which physical form factor is most commonly used for NVMe SSDs in modern laptops and desktops?
Correct! The M.2 form factor has become the dominant standard for NVMe SSDs in consumer devices. It’s a compact, card-style connector that fits directly onto the motherboard, eliminating the need for data and power cables and saving space inside the chassis.
The correct answer is M.2. While 2.5-inch SATA and mSATA were common in older systems, M.2 has taken over as the go-to slot for NVMe drives. U.2 is also used for NVMe but is mostly found in enterprise servers rather than consumer hardware.
Approximately how fast can a high-end PCIe 4.0 NVMe SSD read data sequentially?
Correct! Top-tier PCIe 4.0 NVMe SSDs can achieve sequential read speeds of around 7,000 MB/s. This is a massive leap over SATA SSDs, which are capped near 550 MB/s due to interface bandwidth limitations, and even outpaces many PCIe 3.0 drives significantly.
Not quite — the answer is approximately 7,000 MB/s. Around 550 MB/s is the ceiling for SATA-based SSDs, while 1,200 MB/s is typical for older PCIe 3.0 drives. 20,000 MB/s exceeds even PCIe 5.0 NVMe drives available at time of writing.
What does 3D NAND refer to in modern SSD manufacturing?
Correct! 3D NAND, sometimes called V-NAND by Samsung, stacks memory cells vertically in dozens or even hundreds of layers rather than spreading them flat across a wafer. This dramatically increases storage density without shrinking individual cell sizes, which also helps preserve endurance and reliability.
The correct answer is that 3D NAND stacks memory cells vertically in multiple layers. Planar (2D) NAND arranges cells flat on a single layer, but manufacturers hit physical scaling limits, so the industry moved to vertical stacking to keep increasing capacity without sacrificing cell quality.
Which interface protocol were most SATA SSDs designed to use before NVMe became mainstream?
Correct! AHCI (Advanced Host Controller Interface) is the protocol that SATA SSDs communicate over. It was originally designed for mechanical hard drives and supports a single command queue of 32 commands — a major bottleneck compared to NVMe, which supports 65,535 queues each holding 65,535 commands.
The answer is AHCI, which stands for Advanced Host Controller Interface. SCSI and IDE are much older standards largely retired from consumer use, while NVMe is the newer protocol used by PCIe-based drives. AHCI’s single command queue made it a poor fit for the parallelism flash storage can deliver.
Which NAND type offers the highest storage density per chip but typically has the lowest endurance?
Correct! QLC, or Quad-Level Cell NAND, packs four bits into every cell, giving it the highest density of common consumer NAND types. The trade-off is significantly reduced endurance — QLC cells wear out faster because of the precision needed to distinguish between 16 different voltage states per cell.
The answer is QLC (Quad-Level Cell). It stores 4 bits per cell, making it the densest and most affordable NAND type, but it also has the lowest P/E (program/erase) cycle endurance. SLC sits at the opposite end — fewest bits per cell but the longest lifespan.
Which PCIe generation, first adopted widely in consumer SSDs around 2020, doubled the bandwidth of its predecessor?
Correct! PCIe 4.0 arrived in consumer platforms around 2020, starting with AMD’s Ryzen 3000 series and X570 motherboards. It doubles the per-lane bandwidth compared to PCIe 3.0, pushing NVMe SSD sequential speeds from roughly 3,500 MB/s up to around 7,000 MB/s.
The correct answer is PCIe 4.0, which first appeared broadly in consumer hardware around 2020 with AMD’s Zen 2 platform. PCIe 3.0 was the previous mainstream standard, while PCIe 6.0 is a more recent enterprise-focused generation not yet common in everyday consumer motherboards.
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To bypass this inherent bottleneck, manufacturers allocate a specific portion of that high-capacity memory to act as a temporary, high-speed buffer. The drive’s controller treats this allocated section as if it were single-level cell memory, meaning it only writes a single bit of data to each cell. Writing just one bit is incredibly fast and requires far less precision. When you save a file or install a program, the data is first rapidly absorbed by this single-level cell cache at the maximum advertised speed. Once your computer enters an idle state, the drive quietly goes to work in the background, carefully transferring that data from the fast cache into the denser, slower main storage area to free up the buffer for your next task. This dynamic system pretty much just hides the true, slower write speeds of the underlying memory chips from the user, presenting the illusion of a premium storage device. Like a premium SSD, but cheaper.
7/10
- Storage capacity
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1TB, 2TB, 4TB, 8TB
The Samsung 9100 PRO NVMe SSD offers read speeds of up to 14.7GB/s and write speeds of up to 13.4GB/s, and it hits the mark. As the fastest SSD available as of March 2025, the 9100 PRO is made with professionals in mind. Designed to enhance AI workflows, as well as boost the speed of video and photo editing and exports, this SSD is purpose-built to help improve your efficiency.
How much of a difference does it make?
A dramatic performance boost during everyday computing
Frankly, if you were to force a standard consumer drive to write directly to its native dense memory without any buffer, the process would feel noticeably sluggish. If you have SLC caching, though, it temporarily buffers incoming data so rapidly that it practically eliminates storage bottlenecks during typical computer usage. For the vast majority of consumers, this means the difference is nothing short of night and day.
Consider the tasks that make up a normal daily workflow. Booting up your operating system, launching a web browser, opening a spreadsheet, or saving a few high-resolution photographs are all relatively small, bursty operations. Because the data involved in these actions easily fits within the designated high-speed buffer, the drive can execute these commands almost instantaneously, often reaching speeds of several gigabytes per second on modern hardware. You get to enjoy the full, advertised capabilities of your drive every single time you sit down to work or play. Even modern video games, which can require loading gigabytes of textures and audio files into system memory, benefit immensely from this architecture, resulting in dramatically reduced loading screens.
As long as your workload consists of these short, intense bursts of activity followed by brief periods of rest, the solid-state drive will feel like an absolute powerhouse. The caching system is so highly optimized that average users will likely never realize they are relying on a temporary buffer. Pretty cool stuff, right?
It has disadvantages, too
The severe limitations behind the high-speed illusion
While the benefits of this high-speed buffer are undeniable for everyday tasks, the architecture inherently possesses severe limitations that become glaringly apparent under heavy workloads. The primary disadvantage stems from the simple fact that the cache is finite. Depending on the specific drive, this fast zone might only account for a small percentage of the total storage capacity. Once you attempt to transfer a massive amount of data in a single, continuous operation—such as backing up an entire hard drive, exporting a feature-length high-definition video, or installing a massive modern video game directory—you will quickly exhaust that available high-speed space. It’s just trying to play the part of an ultra-fast SSD, even though it’s really not.
When the buffer reaches its maximum capacity, the illusion of premium performance immediately shatters. The drive’s controller is suddenly forced to perform a highly complex juggling act. It must continue accepting incoming data from your computer while simultaneously flushing the existing cached data into the slower, dense storage memory to make room. This intense dual workload drastically reduces the overall throughput of the drive. The write speeds will plummet from the advertised gigabytes per second down to a mere fraction of that performance, often dropping to speeds that rival outdated mechanical hard drives.
Furthermore, the size of this temporary buffer is frequently dynamic, meaning it shrinks as your drive fills up with permanent files. If your drive is hovering near maximum capacity, the available cache becomes incredibly small, making it far more likely that you will hit this severe performance wall even during moderate file transfers.
Understand your drive’s true limits
SLC caching is a brilliant engineering workaround that makes affordable storage feel incredibly fast. However, recognizing this illusion helps you understand why performance suddenly drops during massive file transfers and why keeping your drive from filling up completely is essential for optimal speed.
- Storage capacity
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2TB
- Hardware Interface
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PCIe Gen4x4
The WD_BLACK SN850X is even faster than the SN850 it replaces, making it an even better option for your PlayStation 5. The Sony-recommended heat sink helps ensure that your drive will last just as long as your PS5 does.
Stephan is the sports journalist for the Maple Grove Report.
