A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently.
It is sometimes called semiconductor storage device, solid-state device, or solid-state disk.
SSDs rely on non-volatile memory, typically NAND flash, to store data in memory cells. The performance and endurance of SSDs vary depending on the number of bits stored per cell,
ranging from high-performing single-level cells (SLC) to more affordable but slower quad-level cells (QLC). In addition to flash-based SSDs, other technologies such as 3D XPoint
offer faster speeds and higher endurance through different data storage mechanisms.
Unlike traditional hard disk drives (HDDs), SSDs have no moving parts, allowing them to deliver faster data access speeds,
reduced latency, increased resistance to physical shock, lower power consumption, and silent operation.
Often interfaced to a system in the same way as HDDs, SSDs are used in a variety of devices, including personal computers, enterprise servers, and mobile devices. However,
SSDs are generally more expensive on a per-gigabyte basis and have a finite number of write cycles, which can lead to data loss over time. Despite these limitations,
SSDs are increasingly replacing HDDs, especially in performance-critical applications and as primary storage in many consumer devices.
Attributes
An SSD stores data in semiconductor cells, with its properties varying according to the number of bits stored in each cell (between 1 and 4).
Single-level cells (SLC) store one bit of data per cell and provide higher performance and endurance. In contrast, multi-level cells (MLC), triple-level cells (TLC), and quad-level cells (QLC) store more data per cell but have lower performance and endurance
. SSDs using 3D XPoint technology, such as Intel's Optane, store data by changing electrical resistance instead of storing electrical charges in cells, which can provide faster speeds and longer data persistence compared to conventional flash memory.
SSDs based on NAND flash slowly leak charge when not powered, while heavily-used consumer drives may start losing data typically after one to two year in storage. SSDs have a limited lifetime number of writes, and also slow down as they reach their full storage capacity.
SSDs also have internal parallelism that allows them to manage multiple operations simultaneously, which enhances their performance.
Unlike HDDs and similar electromechanical magnetic storage, SSDs do not have moving mechanical parts, which provides advantages such as resistance to physical shock,
quieter operation, and faster access times. Their lower latency results in higher input/output rates (IOPS) than HDDs.
Some SSDs are combined with traditional hard drives in hybrid configurations, such as Intel's Hystor and Apple's Fusion Drive. These drives use both flash memory and spinning magnetic disks in order to improve the performance of frequently-accessed data.
Traditional interfaces (e.g. SATA and SAS) and standard HDD form factors allow such SSDs to be used as drop-in replacements for HDDs in computers and other devices. Newer form factors such as mSATA, M.2, U.2, NF1/M.3/NGSFF, XFM Express (Crossover Flash Memory, form factor XT2)
and EDSFF and higher speed interfaces such as NVM Express (NVMe) over PCI Express (PCIe) can further increase performance over HDD performance.
