What is an SSD?
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Short answer
An SSD (solid-state drive) stores data on NAND flash memory chips instead of spinning magnetic platters. With no moving parts, it reads and writes much faster than a hard drive. SSDs come in different shapes (2.5-inch, M.2) and connect over different interfaces (SATA or NVMe over PCI Express) — and those two choices decide what fits your computer.
What is inside
- NAND flash holds the data. Cells store one or more bits each: three bits per cell is called TLC, four is QLC. Samsung describes the 870 EVO’s flash as “V-NAND 3bit MLC” (TLC) and the 870 QVO’s as “4bit MLC” (QLC) (Samsung brochure).
- A controller manages where data is written, spreads wear across the cells and runs background tasks such as garbage collection and TRIM (Samsung 870 EVO datasheet).
- A DRAM cache on many drives holds the map of where data lives. The 870 EVO 1TB has 1GB of LPDDR4. Drives without DRAM may borrow a little of the computer’s memory instead (Host Memory Buffer, HMB). Not every device supports that — Sony states the PS5 does not support HMB (Sony).
Form factors
| Form factor | Size | Example |
|---|---|---|
| 2.5-inch | 100 × 69.85 × 6.8 mm | Samsung 870 EVO |
| M.2 2280 | 22 mm wide, 80 mm long | WD_BLACK SN850X |
M.2 drives come in other lengths too. The PS5’s expansion slot, for example, accepts M.2 types 2230, 2242, 2260, 2280 and 22110 (Sony).
Interfaces
- SATA — the same connection hard drives use, limited to 6 Gb/s. SATA SSDs are rated at about 560 MB/s.
- NVMe — a protocol designed for flash, running over PCI Express. A PCIe 4.0 x4 drive such as the SN850X is rated at up to 7,300 MB/s.
The full comparison: NVMe vs SATA. SSDs against hard drives: SSD vs HDD.
Endurance: TBW
Flash cells wear with each write. Manufacturers state the expected life as TBW — total terabytes written. Samsung defines it as “the total amount of data that can be written on an SSD before it is likely to fail”, and rates the 870 EVO 1TB at 600 TBW, tested to the JEDEC JESD218 standard. Larger drives get higher ratings: the WD_BLACK SN850X goes from 600 TBW at 1TB to 4,800 TBW at 8TB (Sandisk).
Capacity: why a 1TB drive shows less
Drive makers count 1TB as one trillion bytes; Windows counts in binary units and part of the space is used for the file system. Both Samsung and Sandisk note that usable capacity is less than the label.
FAQ
Is an SSD faster than a hard drive? Yes, by manufacturer ratings: about 560 MB/s for SATA SSDs and several thousand MB/s for NVMe, against roughly 190–220 MB/s for a 3.5-inch desktop hard drive.
Do I need a heatsink? Many M.2 NVMe drives are sold with and without one. The PS5 requires a cooling structure on the drive (Sony); in desktops, many motherboards include M.2 heatsinks.