An internal SSD, or solid-state drive, is a storage device that uses NAND-based flash memory to store data on a computer or other digital device. Unlike traditional hard disk drives (HDDs) which use spinning disks to read and write data, SSDs use flash memory chips to store and retrieve data. This makes SSDs faster and more reliable than HDDs, as they have no moving parts that can break or wear out.

SSDs come in different form factors and interface standards, including 2.5-inch SATA, M.2 NVMe, and PCIe. SATA SSDs are the most common type, and they are compatible with most desktop and laptop computers. M.2 NVMe and PCIe SSDs are faster than SATA SSDs, but they require a compatible motherboard or expansion card to work.

The main advantage of SSDs over HDDs is speed. SSDs can read and write data much faster than HDDs, which makes them ideal for tasks that require high-speed data access, such as booting up a computer, launching applications, and transferring large files. SSDs also have lower latency and higher random access speeds, which means that they can access and retrieve data more quickly than HDDs.

When choosing an SSD, there are several factors to consider, including capacity, speed, endurance, and price. Most SSDs come in capacities ranging from 128GB to 2TB or more, with larger capacities generally costing more. Speed is also an important factor, with higher read and write speeds generally resulting in better performance. Endurance refers to the number of program-erase cycles an SSD can handle before it begins to fail, and is measured in total bytes written (TBW).

Some of the main SSD brands include Samsung, Western Digital, Seagate, Kingston, Crucial, Intel, and SanDisk. Each brand offers different SSD models with varying capacities, speeds, and features, so it's important to do research and choose the one that best meets your needs and budget.