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. Etymologically, "solid-state drive" partly refers to existing data storage devices like tape drives and hard disk drives, which all use a mechanically driven storage medium.
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.
SSDs come in various form factors and interface types, including SATA, PCIe, and NVMe, each offering different levels of performance. Hybrid storage solutions, such as solid-state hybrid drives (SSHDs), combine SSD and HDD technologies to offer improved performance at a lower cost than pure SSDs.
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 years unpowered 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/NGFF, 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.
Comparison with other technologies
Hard disk drives
Traditional HDD benchmarks tend to focus on the performance characteristics such as rotational latency and seek time. As SSDs do not need to spin or seek to locate data, they are vastly superior to HDDs in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. Therefore, SSD testing typically looks at when the full drive is first used, as the new and empty drive may have much better write performance than it would show after only weeks of use.
The reliability of both HDDs and SSDs varies greatly among models. Some field failure rates indicate that SSDs are significantly more reliable than HDDs. However, SSDs are sensitive to sudden power interruption, sometimes resulting in aborted writes or even cases of the complete loss of the drive.
Most of the advantages of solid-state drives over traditional hard drives are due to their ability to access data completely electronically instead of electromechanically, resulting in superior transfer speeds and mechanical ruggedness. On the other hand, hard disk drives offer significantly higher capacity for their price.
In traditional HDDs, a rewritten file will generally occupy the same location on the disk surface as the original file, whereas in SSDs the new copy will often be written to different NAND cells for the purpose of wear leveling. The wear-leveling algorithms are complex and difficult to test exhaustively. As a result, one major cause of data loss in SSDs is firmware bugs.
+ Comparison of NAND-based SSD and HDD Attribute or characteristic Solid-state drive (SSD) Hard disk drive (HDD) Price per capacity SSDs are generally more expensive than HDDs and are expected to remain so. As of late 2025, SSD prices are around $0.05-0.10 per gigabyte for 4TB and 8TB models. HDDs, as of late 2025, are priced around $0.01 to $0.03 per gigabyte for 4TB and 8TB models. Storage capacity As of 2026, SSDs are available in sizes up to 512 TB, though most PCs run models ranging from 1TB to 4TB. HDDs of up to 36 TB are available as of 2025. Reliability – data retention If the nominal written life of SSDs (the terabytes written) is reached, the SSDs may start losing data after three months (enterprise SSDs) or one year (consumer SSDs) without power, especially at high temperatures. Newer SSDs, depending on usage, may retain data longer. SSDs are generally not suited for long-term archival storage. HDDs, when stored in a cool, dry environment, can retain data for longer periods without power. However, over time, mechanical parts may fail, such as the inability to spin up after prolonged storage. Reliability – longevity SSDs lack mechanical parts, theoretically making them more reliable than HDDs. However, SSD cells wear out after a limited number of writes. Controllers help mitigate this, allowing for many years of use under normal conditions. HDDs have moving parts prone to mechanical wear, but the storage medium (magnetic platters) does not degrade from read/write cycles. Studies have suggested HDDs may last 9–11 years. Start-up time SSDs are nearly instantaneous, with no mechanical parts to prepare. HDDs require several seconds to spin up before data can be accessed. Sequential-access performance As of mid-2026, Consumer SSDs can offer transfer rates between 500 MB/s (SATA Gen3) to 15000 MB/s (PCIe NVMe Gen5), depending on the model. Micron 9650 is the first Gen6 SSD and can reach 28 GB/s in sequential read speeds. As of mid-2026, HDDs can transfer data at approximately 100 MB/s (2.5" SATA HDD) to 300 MB/s (3.5" SATA HDD). Rotational disks are generally fastest if data is located towards the outside of a platter. For optimal throughput, use the first and empty partition. Random-access performance SSD random access times typically range from 0.05-0.2 ms (50-200 microseconds) for consumer NAND SSDs, with NVMe drives achieving 0.05-0.1 ms and SATA SSDs around 0.5-0.6 ms. HDD random access times range from 2.9 ms (high-end) to 12 ms (laptop HDDs). Power consumption High-performance SSDs use about half to a third of the power required by HDDs. HDDs use between 2 and 5 watts for 2.5-inch drives, while high-performance 3.5-inch drives can require up to 20 watts. Acoustic noise SSDs have no moving parts and are silent. Some SSDs may produce a high-pitched noise during block erasure. HDDs generate noise from spinning disks and moving heads, which can vary based on the drive's speed. Temperature control SSDs generally tolerate higher operating temperatures and generally do not require special cooling. HDDs need cooling in high-temperature environments (above ) to avoid reliability issues.
Memory cards
While both memory cards and most SSDs use flash memory, they have very different characteristics, including power consumption, performance, size, and reliability. Originally, solid state drives were shaped and mounted in the computer like hard drives. In contrast, memory cards (such as Secure Digital (SD), CompactFlash (CF), and many others) were originally designed for digital cameras and later found their way into cell phones, gaming devices, GPS units, etc. Most memory cards are physically smaller than SSDs, and designed to be inserted and removed repeatedly.
Failure and recovery SSDs have different failure modes from traditional magnetic hard drives. Because solid-state drives contain no moving parts, they are generally not subject to mechanical failures. However, other types of failures can occur. For example, incomplete or failed writes due to sudden power loss may be more problematic than with HDDs, and the failure of a single chip may result in the loss of all data stored on it. Nonetheless, studies indicate that SSDs are generally reliable, often exceeding their manufacturer-stated lifespanFlash Reliability in Production: The Expected and the Unexpected – Schroeder, Lagisetty & Merchant, 2016. and have lower failure rates than HDDs. However, studies also note that SSDs experience higher rates of uncorrectable errors, which can lead to data loss, compared to HDDs.
The endurance of an SSD is typically listed on its datasheet in one of two forms: either n DW/D (n drive writes per day) or m TBW (maximum terabytes written), abbreviated TBW. For example, a Samsung 970 EVO NVMe M.2 SSD (2018) with 1 TB of capacity has an endurance rating of 600 TBW.
The basic parameter for determining the lifespan of Flash-NAND systems is the number of programming-erase (P/E) cycles. The TBW parameter is the product of the P/E cycle resource and the SSD capacity. For an SSD with a capacity of 1 TB and TBW = 600 TB, the number of P/E cycles is 600.
Recovering data from SSDs presents challenges due to the non-linear and complex nature of data storage in solid-state drives. The internal operations of SSDs vary by manufacturer, with commands (e.g. TRIM and the ATA Secure Erase) and programs (e.g. hdparm) being able to erase and modify the bits of a deleted file.
Reliability metrics The JEDEC Solid State Technology Association (JEDEC) has established standards for SSD reliability metrics, which include: Unrecoverable Bit Error Ratio (UBER) Terabytes Written (TBW) – the total number of terabytes that can be written to a drive within its warranty period Drive Writes Per Day (DWPD) – the number of times the full capacity of the drive can be written to per day within its warranty period
Applications In a distributed computing environment, SSDs can be used as a distributed cache layer that temporarily absorbs the large volume of user requests to slower HDD-based backend storage systems. This layer provides much higher bandwidth and lower latency than the storage system would, and can be managed in a number of forms, such as a distributed key-value database and a distributed file system. On supercomputers, this layer is typically referred to as burst buffer.