As of 2010, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile random-access memory (RAM) also exist for situations that require even faster access, but do not necessarily need data persistence after power loss, or use external power or batteries to maintain the data after power is removed.
A hybrid drive combines the features of an HDD and an SSD into one unit, containing a large HDD and a smaller SSD cache to improve performance of frequently accessed files. These can offer near-SSD performance in most applications (such as system startup and loading applications) at a lower price than an SSD. These are not suitable for data-intensive work, nor do they offer the other advantages of SSDs.
Battery or super capacitorAnother component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed. In the case of MLC flash memory, a problem called lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.
Host interfaceThe host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller discussed above. The interface is generally one of the interfaces found in HDDs. They include:
Comparison of SSD with hard disk drivesHDDs is difficult. Traditional HDD benchmarks are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.
Most advantages of solid-state disks over traditional hard drives come from the characteristic of data being accessed completely electronically instead of an electro-mechanical machine. On the other hand, traditional hard drives currently excel by offering much more capacity for the same price.
While SSDs appear to be more reliable than HDDs, researchers at the Center for Magnetic Recording Research "are adamant that today's SSDs aren't an order of magnitude more reliable than hard drives". If and when an SSD fails, the failure is likely to be catastrophic with total data loss. HDDs can fail in this way too, but often give warning that they are failing, allowing much or all of their data to be recovered. One cause of data loss in current generation of SSDs is firmware bugs, which in HDDs rarely cause problems.
No Crash file during power lost.
Watch this video for real comparison.
A Samsung SDD