What does SSD mean?

For most of our technological history, computers and similar devices have used mechanical hard drives (HDDs) to manage data. These could store large amounts of data, had decent speeds, and simply did what they were supposed to do for the time. However, today, SSDs have almost completely replaced HDDs in terms of functionality unless you are aiming for long-term or inexpensive storage.

The term SSD means solid state drive. The “solid state” part refers to the fact that, unlike a hard drive, there are no moving parts, such as a read/write head or spinning disk. Instead, an SSD is a single solid board on which data is stored electronically in the form of trapped electrons. One of the things that makes SSDs more reliable than hard drives is the lack of moving parts. Similar to hard drives, SSDs are also a type of non-volatile memory, meaning that stored data is not lost when you stop powering the SSD. This is different from RAM, where temporary data is erased as soon as you disconnect a power supply.

To understand what makes SSDs so special, we need to talk about how data is stored on a hard drive. In a traditional hard drive, it is stored as magnetic patterns on a physical disk. A mechanical read/write head moves across the disk as it spins, writing or reading data as needed.

In an SSD, there are no moving parts. Instead, data is stored as electrical charges in flash memory cells. When you download something or write new data to an SSD, the number of electrons in these cells changes. To access the data, the reader measures the electrical charge in each cell and converts it to binary. Handling data via electrons is much faster than using a read/write head, because mechanical parts always introduce some form of latency. This is why even a cheap SATA SSD is much faster than a hard drive, being capable of transferring data at a rate of 550 MB/s. NVMe SSDs go even further, with major SSD manufacturers producing drives supporting speeds of up to 14,000 MB/s (14 GB/s) for PCIe Gen 5.0. For comparison, a traditional hard drive maxes out at around 160MB/s.

Early SSDs used single-level cell technology, which meant that each cell represented a single bit of data. SSDs that use it are still the fastest and most durable, but they are also much more expensive than modern alternatives that use a multi-level cell, a three-level cell, or a four-level cell. The price, speed, and lifespan of an SSD decrease as the number of bits represented by each cell increases.

SATA stands for Serial Advanced Technology Attachment and refers to both the storage interface and physical connection used by hard drives and most older or cheaper SSDs. The SATA storage interface has a single lane for data transit and reaches a maximum of 550 MB/s in actual usage. This is more than enough for a hard drive but creates a bottleneck for SSDs. PCIe, or Peripheral Component Interconnect Express, is another type of storage interface, much faster than SATA. It has several routes. Drives that connect directly to PCIe are significantly faster because they can directly use the processor’s processing power. This is what allows NVMe drives to reach write speeds of up to 14,000 MB/s in the latest generations.

It’s easy to think of the SATA interface and the physical SATA connection as one and the same, but that’s not always true. Most SATA SSDs come in a 2.5-inch form factor, but there are also M.2 SATA SSDs that plug directly into your motherboard’s M.2 slot. These look similar to NVMe drives, but despite the visual similarity, they are still tied to the 550 MB/s restriction.

Finally, NVMe refers to Non-Volatile Memory Express, which is a protocol or data transfer language designed from the ground up to take advantage of PCIe speeds. M.2 is the thin, stick-shaped form factor that NVMe drives are typically available in. If you’re not sure how to tell the difference between a SATA SSD and an NVMe SSD when they’re both M.2, you can tell them apart based on their notches: SATA SSDs have two notches, while an NVMe only has one.