An SSD (solid-state drive) is a storage device that keeps data in NAND flash memory chips with no moving parts. Because nothing spins or seeks, an SSD answers requests in microseconds where a hard drive takes milliseconds, survives drops and vibration, runs silent, and draws less power. It is the reason a modern computer boots in seconds.
How an SSD works
Two components define every SSD: NAND flash, which stores the bits, and a controller, which decides where every piece of data lives, spreads writes across the flash so it wears evenly, corrects errors, and talks to your computer over the drive’s interface. Most drives also dedicate a slice of flash as a fast cache to absorb bursts of writes. The quality of the controller and its firmware separates great drives from cheap ones far more than the flash itself, which is why two drives with identical spec-sheet numbers can behave very differently under sustained load.
Why SSDs are faster than hard drives
The headline numbers are sequential: a PCIe Gen5 SSD moves data at up to roughly 15GB/s versus about 275MB/s for the fastest hard drives. But the difference that changes how a computer feels is latency and parallelism: an SSD services thousands of scattered small requests simultaneously while a hard drive’s single actuator handles them one seek at a time. That is why an SSD transforms boot, application launch, and game load times even when file copies look only modestly faster. For the full comparison, see SSD vs HDD.
Form factors and interfaces
Most consumer SSDs are M.2 sticks that slot directly onto the motherboard and speak NVMe over PCIe. Gen4 drives like the Samsung 990 cover the value tier, while Gen5 drives are the performance mainstream, reaching 8TB in models like the Samsung 9100 Pro. External SSDs put the same flash behind USB or Thunderbolt. Datacenters use ruler-style EDSFF drives built for density and airflow rather than the 2.5-inch cases inherited from disks.
Endurance: how long an SSD lasts
Flash cells wear as they are written, so drives carry an endurance rating: TBW (terabytes written) for consumer models, drive writes per day for enterprise. In practice a mainstream user will not exhaust a modern TLC drive’s rating within the useful life of the computer. Controllers manage wear automatically, and drive health is visible in any SMART utility.
When a hard drive is still the right answer
Cost per terabyte. Bulk media libraries, backup targets, surveillance, and archives measured in tens of terabytes still belong on spinning disks, where drives like the 32TB Seagate IronWolf Pro deliver capacity flash cannot touch at the price. The right build is usually both: an SSD for everything you run, hard drives for everything you keep.
Which SSD should you buy?
Our Leaderboard carries current lab-tested picks for every budget and use case, from value Gen4 to flagship Gen5 and enterprise drives, updated as new reviews publish. For the deeper technology background, start with the SSD Reference Guide and SSD Glossary.
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