When you're in the market for a new SSD, you're probably focusing on the PCIe interface (PCIe 4.0 or PCIe 5.0) and the read/write speeds. Most people choose a reasonably priced PCIe 4.0 NVMe SSD for their PC, and the one spec they might check is the read/write speed. That's where the research ends in most cases, but it's important to know a few other things about the drive you're buying. Whether it has DRAM or not, how long it can last, and what type of NAND it uses are vital questions that should be answered before you part with your money.

Endurance

Nothing lasts forever

Endurance of an SSD refers to the amount of data that can be written to it before it starts experiencing reduced performance, increased error rates, and eventual failure. It is usually measured in TBW or terabytes written, and is one of the easier SSD specs to find. If it's not mentioned on the product page, you can check third-party websites that keep a database of SSD information. Most 1TB SSDs have a 600TBW rating, which is enough to last you 5 to 6 years, even if you write absurd amounts of data to it every day.

SSD flash memory doesn't last forever, and the TBW or MTBF (mean time between failures) ratings give you an idea about the life you can expect out of a drive. SSDs with larger capacities have higher TBW ratings, since there are more cells for the SSD to distribute the write operations, reducing the wear on individual cells. You might be reducing your SSD's lifespan unknowingly by depriving it of sufficient cooling, not using the built-in protections, and ignoring SSD heatsinks for high-performance drives.

Type of NAND flash

Not all flash memory is made equal

The NAND flash memory on SSDs is responsible for storing your data, and it comes in various types. Depending on the cost of an SSD, the manufacturer will choose to use one of four major NAND types. SLC NAND stores one bit per cell, and is the fastest and most durable. It's also the costliest to manufacture, which is why you'll only see it in server and enterprise SSDs. MLC, TLC, and QLC NAND stores two, three, and four bits per cell, respectively. Performance and cost reduce as you go from MLC to QLC NAND.

MLC and TLC NAND are used on the best consumer drives, while QLC NAND is seen on cost-effective drives that aren't known for their performance. Before you're tempted to opt for a cheap, entry-level SSD, make sure to avoid the QLC NAND options if you can. They tend to slow down faster than other SSDs, and can also develop faults faster than other SSDs. Various high-capacity SSDs use QLC NAND to target use cases where speed might be secondary.

DRAM cache

Ace up the sleeve

You might have seen some manufacturers advertise DRAM on their SSDs. This is a high-speed memory buffer used to speed up SSD operations by storing frequently accessed data. SSDs with DRAM are usually more expensive than those without it, but DRAM cache can come in handy in certain use cases. You might not notice its benefits during gaming or day-to-day usage, but it comes into play when transferring large amounts of data.

If you're a prosumer needing to move tons of data around frequently, investing in a DRAM SSD is worth it. While DRAM-less SSDs have gotten way better at using Host Memory Buffer (HMB) — substituting system RAM for onboard DRAM — you should still opt for a DRAM SSD if it isn't significantly pricier than a DRAM-less alternative.

Controller quality

The command center

Every SSD has a controller that's responsible for communicating with the PC, and determining a lot of the drive's performance. It's a dedicated chip on the SSD that manages all the read/write operations and organizes the data in the memory. Higher-quality drives will inevitably have more performant and advanced controllers, but it's still advisable to do your research before choosing an SSD. Although it's relatively harder to locate this specification, you can check third-party reviews or the manufacturer's website.

There are several controller brands, such as Samsung, Intel, WD, SK Hynix, Phison, Realtek, Marvell, and SMI. Brands like Samsung, Intel, SK Hynix, and WD use their own controllers on their SSDs, while others feature controllers from other manufacturers. You don't need to get into the details of multiple controllers, but knowing whether a controller is top-of-the-line, mid-range, or entry-level can be helpful when comparing different SSDs.

Random IOPS

Look beyond sequential speeds

The only read/write speeds advertised by SSD manufacturers are the sequential speeds — the sky-high numbers you see breaching 14,000MB/s on the latest PCIe 5.0 SSDs. Although these numbers look nice, they're not of much help when you need to get an idea of the real-world performance of an SSD in the most common use cases. While sequential speeds account for large data transfers, random IOPS (Input/Output Operations Per Second) indicate the performance you can expect in gaming and general desktop use.

Again, you'll need to refer to third-party reviews or SSD database websites to check the random IOPS number for the SSD you want to buy. You'll usually see numbers of around 1.6 million IOPS for high-end Gen4 drives like the Samsung 990 Pro, and around half that for models like the WD Black SN770. Although random IOPS don't tell the full picture, it can be an additional metric to compare the drives in your shortlist.

Don't buy the wrong SSD

With so many SSDs on the market, it's easy to overpay for an inferior product. Even SSDs with the same PCIe interface don't feature the same performance or longevity. While it's always a must to refer to third-party reviews before buying a drive, having an idea of the most important SSD specs leaves you in a better position when comparing multiple options. A few of these specs can make or break your decision, especially if the SSDs on your shortlist are closely tied in almost every department.