What does 3D NAND or TLC NAND mean? How do you choose the best SSD for your PC? These questions may burn in the minds of those seeking additional storage, which is where this explainer piece will help clear up some of the jargon. I'll run through what a solid-state drive (SSD) is, how it works compared to a mechanical hard drive, and what you need to know about choosing the right one based on published specifications.

What is an SSD and how does it work?

Getting inside the flash storage

An SSD is simply memory chips soldered onto a PCB. A controller handles everything and there may even be some cache and local memory to help with performance. Interfaces like SATA, USB, or PCIe allow the drive to connect with the motherboard and other PC parts. Where an SSD differs from a mechanical drive is the lack of any moving parts. Instead of using spinning platters and actuator arms with magnets, an SSD uses NAND memory chips that require power.

Because of this difference, an SSD is better suited to laptops and other portable devices, including your smartphone. It's also great for storing data on a desktop PC with faster transfer speeds and higher bandwidth for larger files, which are commonplace with modern games and software. When you move a file to an SSD, it's digitally sent to the controller, which decides where all the bytes of data are stored on the memory modules. Unlike RAM, data stored on an SSD remains even after power is cut.

What is the best type of SSD memory?

Not all chips are built the same

An SSD has Negative-AND (NAND) or Vertical NAND (V-NAND) to hold all the SLC, MLC, or TLC memory cells. NAND is an older format found on the first generations of solid-state drives and restricted how many cells could be installed and how much data could be saved. Modern drives use V-NAND, allowing cells to be stacked atop one another. The more cells present on the PCB, the more capacity the drive will have to offer. NAND-based storage such as SSDs has error-correcting code (ECC) to check all data is written and read without errors.

You'll often come across MLC, SLC, and TLC acronyms so let's look at the available memory cell types:

Single-level cell (SLC): The most expensive form of NAND for SSDs is single-level cells. These hold one bit of data each, and are the fastest and most durable form of flash memory, but are often found on the most expensive drives. They're incredibly reliable, should last a long time, and don't require as much power.

Multi-level cell (MLC): Next up are multi-level cells. As suggested by the name, these can hold two bits of data per cell, allowing for far larger capacities over single-level cell SSDs without physically increasing the size of the drive. SSDs with MLC chips will be more affordable, but have slower transfer rates and won't be as long-lasting as SLC drives. MLC is better for storing the operating system, files, and documents.

Triple-level cell (TLC): Then there's the triple-level cell. Three bits of data can be held by each cell, allowing for some incredibly large SSDs for reasonable prices. Like MLC SSDs, these drives will suffer from slower read and write speeds, and weaker endurance.

SLC SSDs are designed for heavier usage. Think servers, NAS, and systems with software that writes a good amount of data. They're more expensive than other memory cell types but are incredibly reliable and solid for long-term use. That's not to say MLC and TLC drives will fail in record time, but you can expect an SLC SSD to last. An MLC drive is slightly more affordable and can hold more data, but it's slower and doesn't do too well with lots of data being written. TLC is the most affordable yet offers the best capacities and is great for storing big files (and lots of them).

What are the different SSD interfaces?

Connecting your data to your PC

A few interfaces are available for connecting an SSD to a motherboard. These include NVMe, PCIe, SATA III, and USB. USB is the most popular for external SSDs, SD cards, and USB flash drives. M.2 slots are used by thin SSDs and can be either SATA III or NVMe (PCIe). 2.5-inch SSDs connect to an available SATA III port. Here's all you need to know about them:

Serial ATA (SATA): SATA has been around for years and is still used today. Depending on the form factor, SATA SSDs can use either an M.2 slot or cable header on the motherboard.

Universal Bus (USB): USB drives connect to an available port on the PC. These drives are often the slowest due to connection limitations with USB. SD cards are included here with adapters.

Peripheral Component Interconnect Express (PCIe): PCIe SSDs don't use the same SATA connection and instead use one of the available PCI lanes from the processor. This allows the drives to run at faster speeds, though you will get the best results with an NVMe PCIe drive.

Non-Volatile Memory Express (NVMe): This is the newest and greatest form of storage technology. Designed for SSDs and using PCI lanes, NVMe allows the SSD to take requests from multiple processor cores. The fastest (and most expensive) drives available are NVME PCIe SSDs.

Modern motherboards usually have a collection of SATA III ports (four to eight) for 2.5-inch SSDs and mechanical drives. There will also be a few M.2 slots. More expensive motherboards can have up to six M.2 slots, some even included on an optional PCI expansion card. PCIe NVMe M.2 slots should be used primarily for an operating system drive and storing frequently used apps and games. They should be the first for storing data on your PC, followed by secondary SATA M.2 slots for slower SSDs.

Finally, the available SATA III ports can be used. I recommend using them as a last resort unless seeking the most affordable SSDs. They require power, which needs to be fed directly from the PSU instead of the motherboard, requiring an additional cable.

Choosing the best SSD for your PC

Now that you're armed with all the necessary information to choose the right SSD, the endless sea of options will appear far less daunting. We've been reviewing, testing, and writing about flash storage for years and can help you make the right choice for an existing system upgrade or the fastest drive for a new build. So long as you match the form factor with an available connection on the motherboard (M.2 vs. SATA III), you'll have no issues installing the SSD.