A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies as memory to store data persistently. It is also sometimes called solid-state disk.
SSDs have no moving mechanical components. This distinguishes them from traditional electromechanical drives such as hard disk drives (HDDs) or floppy disks, which contain spinning disks and movable read/write heads. Compared with electromechanical drives, SSDs are typically more resistant to physical shock, run silently, have quicker access time and lower latency. However, while the price of SSDs has continued to decline over time, SSDs are (as of 2018) still more expensive per unit of storage than HDDs and are expected to continue to be so into the next decade.
Advantages of SSD over HDD
The standard hard disk drive (HDD) has been the predominant storage device for computers (both desktops and laptops) for a long time. The main draw is the high storage capacity and low cost.
The solid-state drive (SSD) is another storage solution and is slowly replacing the majority of hard disk drives. As you’ll learn by reading the following comparison table, the SSD is a clear winner. However, due to its price per unit of memory, it doesn’t make sense to use SSDs in all instances. For most computer users, we recommend using an SSD as the primary drive for your operating system, as well as the programs you access most frequently. Then, we suggest purchasing a large HDD (either internal or external) for storing documents, pictures, and music.
| Topic | SSD | HDD |
| Access Time | An SSD has access speeds of 35 to 100 micro-seconds, which is nearly 100 times faster. This faster access speed means programs can run more quickly, which is very significant, especially for programs that access large amounts of data often like your operating system. | A typical HDD takes about 5,000 to 10,000 micro-seconds to access data. |
| Price | The price of a solid-state drive is higher than an HDD, which is why most computers with an SSD only have a few hundred gigabytes of storage. Desktop computers with an SSD may also have one or more HDDs for additional storage. | HDD is considerably cheaper than SSD, especially for drives over 1 TB. |
| Reliability | The SSD has no moving parts. It uses flash memory to store data, which provides better performance and reliability over an HDD. | The HDD has moving parts and magnetic platters, meaning the more use they get, the faster they wear down and fail. |
| Capacity | Although there are large SSDs, anything over 1 TB SSD is usually outside of most people’s price range. | Several terabyte hard disk drives are available for very reasonable prices. |
| Power | The SSD uses less power than a standard HDD, which means a lower energy bill over time and for laptops, an increase in battery life. | With all of the parts required to spin the platters, the HDD uses more power than an SSD. |
| Noise | With no moving parts, SSD generates no noise. | With the spinning platters and moving read/write heads, an HDD can sometimes be one of the loudest components in your computer. |
| Size | SSD is available in 2.5″, 1.8″, and 1.0″, increasing the available space available in a computer, especially a desktop or server. | HDDs are usually 3.5″ and 2.5″ in size for desktop and laptops respectively, with no options for anything smaller. |
| Heat | Because there are no moving parts and due to the nature of flash memory, the SSD generates less heat, helping to increase its lifespan and reliability. | With moving parts comes added heat which can slowly damage electronics over time, so the higher the heat, the greater the potential for wear and damage. |
| Magnetism | SSD is not affected by magnetism. | Because a hard drive relies on magnetism to write information to the platter, information could be erased from an HDD using strong magnets. |
| Start-up time | Almost instantaneous; no mechanical components to prepare. May need a few milliseconds to come out of an automatic power-saving mode. | Drive spin-up may take several seconds. A system with many drives may need to stagger spin-up to limit peak power drawn, which is briefly high when an HDD is first started. |
| Random access time | Typically under 0.1 ms. As data can be retrieved directly from various locations of the flash memory, access time is usually not a big performance bottleneck. | Ranges from 2.9 (high end server drive) to 12 ms (laptop HDD) due to the need to move the heads and wait for the data to rotate under the read/write head |
| Impacts of file system fragmentation | There is limited benefit to reading data sequentially (beyond typical FS block sizes, say 4 KB), making fragmentation negligible for SSDs. Defragmentation would cause wear by making additional writes of the NAND flash cells, which have a limited cycle life. However, even on SSDs there is a practical limit on how much fragmentation certain file systems can sustain; once that limit is reached, subsequent file allocations fail | Some file systems, like NTFS, become fragmented over time if frequently written; periodic defragmentation is required to maintain optimum performance. This usually is not an issue in modern file systems. |
| Breather hole | SSDs do not require a breather hole. | Most modern HDDs require a breather hole in order for it to function properly. |