Think of an SSD as a warehouse. Capacity is floor space. The interface is the loading dock: SATA is one narrow door, NVMe over PCIe is a row of wide ones. Sequential speed is how fast full trucks unload. Random speed is how fast staff fetch small items, which is what makes a PC feel quick. The SLC cache is a fast holding bay that fills during big deliveries. Endurance is how many deliveries the building is rated to handle.
The kind of drive: internal SATA SSD, internal NVMe SSD, or portable external SSD.
When it matters: It decides how the drive connects and its speed ceiling. NVMe is far faster than SATA on paper, but for games and everyday use the difference feels small.
How much the drive stores, in GB or TB.
When it matters: Buy capacity before speed. Big modern games can take over 100GB each. Small versions of a model are often slower and rated for fewer writes than the larger ones.
The space Windows shows after formatting, which is less than the box number.
When it matters: Makers count 1TB as 1,000GB while Windows counts in binary units, so a 1TB drive shows about 931GB. This is normal, not missing space.
Skip it if: Always safe to ignore; every drive of the same size shows about the same.
The physical shape: 2.5-inch, M.2 stick (2230, 2242 or 2280 by length), or add-in card.
When it matters: M.2 is a shape, not a speed: M.2 SATA and M.2 NVMe drives look alike. Check the length fits your slot: 2230 for handhelds, 2280 for most desktops.
How the drive connects: SATA, or PCIe with a generation and lane count, such as PCIe 4.0 x4.
When it matters: SATA tops out around 550 MB/s, PCIe 4.0 around 7,000 MB/s and PCIe 5.0 around 14,000 MB/s. A fast drive in an older slot runs at the slot's speed.
The command language the drive uses: NVMe for PCIe drives, AHCI for SATA drives.
When it matters: NVMe handles many requests at once. Some M.2 slots accept only SATA drives, and very old PCs cannot boot from NVMe. Check your board manual.
Skip it if: You already matched the drive to your slot type.
Whether memory chips sit on both sides of an M.2 drive, not just the top.
When it matters: Double-sided drives can be too thick for thin laptops and some handhelds. Desktop slots usually take either kind.
Skip it if: You are installing in a desktop.
Whether the drive meets a game console's storage requirements, such as the PS5 expansion slot.
When it matters: PS5 needs a PCIe 4.0 M.2 NVMe drive with a heatsink that fits the bay height. Xbox Series consoles use their own expansion cards, not standard M.2 drives.
Skip it if: You are buying for a PC.
Top speed reading large continuous files, in MB/s. This is the headline number on the box.
When it matters: Helps when copying big files or opening large video projects. For booting and game loading, drives above SATA speed feel very similar. It is a best-case figure.
Top speed writing large continuous files, in MB/s, measured while the fast cache still has room.
When it matters: It lasts only until the SLC cache fills. After that, cheaper drives can slow sharply, so check sustained write speed for big transfers.
Skip it if: You mostly read data, like a game library drive.
Write speed after the fast cache fills during a long transfer, in MB/s.
When it matters: The honest number for big installs, video recording and large copies. Budget QLC or DRAM-less drives can fall close to hard drive speed here.
Skip it if: You rarely copy large files or install many games at once.
How many small reads or writes per second the drive handles. IOPS means input/output operations per second.
When it matters: Small random reads make a system feel snappy. Box IOPS use ideal deep queues that home use rarely reaches, so treat them as ceilings, not daily speed.
Skip it if: You compare drives of the same class; the gap rarely shows in daily use.
The drive's processor, which manages data, caching and wear. Made by firms like Phison and Silicon Motion, or by the drive brand itself.
When it matters: It sets the drive's performance class and heat. Some models quietly change controller or flash between batches, so an early review may not match a later unit.
A small memory chip that holds the drive's map of where data lives. DRAM-less drives keep that map elsewhere.
When it matters: DRAM helps heavy sustained and mixed workloads and matters most on SATA drives. Modern DRAM-less NVMe drives use Host Memory Buffer and do well for everyday use.
HMB lets a DRAM-less NVMe drive borrow a small slice of system RAM for its data map.
When it matters: It closes most of the gap to drives with DRAM in everyday use. Heavy sustained workloads still favor drives with their own DRAM.
Skip it if: The drive has its own DRAM cache.
The fast buffer where the drive first writes data before moving it to slower flash, in GB.
When it matters: A bigger cache means longer bursts at full speed. The cache shrinks as the drive fills, so a nearly full drive slows down sooner.
Skip it if: Your writes are small, like documents and game saves.
The flash memory type: TLC stores 3 bits per cell, QLC stores 4. More bits per cell is cheaper but slower and less durable.
When it matters: TLC is the mainstream choice. QLC suits big game libraries but slows more on long writes. Samsung markets TLC as '3-bit MLC', so do not read that as true MLC.
Who made the flash chips and how many layers of cells are stacked in each chip.
When it matters: Layer count marks the flash generation, but it does not predict speed alone. The controller and firmware matter more.
Skip it if: You compare using speed, endurance and warranty specs.
Terabytes written (TBW): how much data the maker warrants you can write before the drive may wear out.
When it matters: Typical home use writes far less, so most drives outlast their warranty. Higher TBW suits heavy video work or constant game installs. TBW usually rises with capacity.
Drive writes per day: how many times you can fill the whole drive each day through the warranty.
When it matters: Mainly an enterprise figure. It is the TBW rating expressed another way.
Skip it if: You are a home user; TBW tells you the same thing.
Mean time between failures: a statistical reliability figure in hours, averaged across many drives.
When it matters: It does not mean one drive lasts that long. Figures look similar across drives and are hard to compare. Warranty and TBW say more.
Skip it if: Almost always.
Capacitors that let the drive finish saving data if the power cuts out suddenly.
When it matters: Common on enterprise drives, rare on consumer ones. Matters for servers and data you cannot risk corrupting. A UPS covers most home needs.
Skip it if: You run a typical home or gaming PC and keep backups.
How long the maker covers the drive, in years. It often ends early if you pass the TBW rating.
When it matters: Five years is common on good NVMe drives. Shorter warranties often mark budget models.
Whether the drive comes with a metal cooler, or is sold in a version with one.
When it matters: Fast PCIe 4.0 and 5.0 drives slow down when hot. Use the drive's heatsink or the motherboard's, not both. Check the height in laptops and consoles.
Skip it if: You use a slower drive, or your motherboard slot has its own heatsink.
How much power the drive uses at full load and at rest, in watts.
When it matters: Matters most in laptops and handhelds for battery life and heat. PCIe 5.0 drives draw more and run hotter.
Skip it if: You are building a desktop with decent airflow.
The highest temperature the drive is rated to run at, in Celsius, before it throttles or risks damage.
When it matters: Fast NVMe drives can reach it in cramped slots under a graphics card. Throttling shows up as speed drops during long transfers.
Skip it if: The drive has a heatsink and your case has airflow.
Encryption built into the drive itself, often AES-256 with Opal support for business tools.
When it matters: Useful for business laptops and sensitive data. Software encryption such as BitLocker works on any drive.
Skip it if: You do not need encryption, or you use software encryption.
The maker's app for firmware updates, health checks and cloning an old drive.
When it matters: Firmware updates can fix bugs and speed issues. Free cloning tools save time when moving from an old drive.
Skip it if: You manage drives with other tools.