Attribute or characteristic Solid-state drive Hard disk drive
Spin-up time Almost Instantaneous; nothing mechanical to “spin up”. May need a few milliseconds to come out of an automatic power-saving mode. May take several seconds. With a large number of drives, spin-up may need to be staggered to limit total power drawn.
Random access time About 0.1 ms – many times faster than HDDs because data is accessed directly from the flash memory Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head
Read latency time Generally low because the data can be read directly from any location; In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times Generally high since the mechanical components require additional time to get aligned
Consistent read performance Read performance does not change based on where data is stored on an SSD If data is written in a fragmented way, reading back the data will have varying response times
Fragmentation There is usually very little benefit to reading data sequentially (beyond typical FS block sizes), making fragmentation a void issue for SSDs. Defragmentation process also makes additional writes on the NAND flash cells that already have a limited cycle life. It is also uncertain whether defragmentation would arrange the data in a truly sequential order, as the drive itself can again remap it to various positions. File systems on HDDs may fragment after continued operations of erasing and writing data, especially involving large files. Therefore periodical defragmentation is required to maintain ultimate performance.
Acoustic levels SSDs have no moving parts and make no sound HDDs have moving parts (heads, spindle motor) and have varying levels of sound depending upon model
Mechanical reliability A lack of moving parts virtually eliminates mechanical breakdowns HDDs have many moving parts that are all subject to failure over time
Maintenance of temperature SSDs do not require any cooling maintenance. HDDs require air-forced ventilation to avoid build-up of heat on its body or housing; otherwise, bad sectors on its media can appear later and/or its lifespan will diminish over time.
Susceptibility to environmental factors No flying heads or rotating platters to fail as a result of shock, altitude, or vibration The flying heads and rotating platters are generally susceptible to shock, altitude, and vibration
Magnetic susceptibility No impact on flash memory Magnets or magnetic surges can alter data on the media
Weight and size The weight of flash memory and the circuit board material are very light compared to HDDs Higher performing HDDs require heavier components than laptop HDDs (which are light, but not as light as SSDs)
Parallel operation Some flash controllers can have multiple flash chips reading and writing different data simultaneously HDDs have multiple heads (one per platter) but they are connected, and share one positioning motor.
Write longevity Flash-based SSDs have a limited number of writes (1-5 million or more) over the life of the drive. Software controllers manage this limitation in such a way that drives can last for many decades before failure. SSDs based on DRAM do not have a limited number of writes. Magnetic media do not have a similar limited number of writes but are susceptible to eventual mechanical failure.
Software encryption limitations NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special “Secure Erase” procedures built into the drive. HDDs can overwrite data directly on the drive in any particular sector.
Cost per capacity As of February 2011[update], NAND flash SSDs cost about (US)$.90–2.00 per GB As of February 2011[update], HDDs cost about (US)$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives
Storage capacity As of April 2011[update], SSDs come in different sizes up to 2TB but are typically not larger than 64-256GB, due to their high cost per GB. As of April 2011[update], HDDs are typically 500GB-1TB but drives as large as 2 or 3 TB are also available.
Read/write performance symmetry Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have a balanced read and write speed. HDDs generally have slightly lower write speeds than their read speeds.
Free block availability and TRIM SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance. HDDs are not affected by free blocks or the operation (or lack) of the TRIM command
Power consumption High performance flash-based SSDs generally require 1/2 to 1/3 the power of HDDs; High performance DRAM SSDs generally require as much power as HDDs and consume power when the rest of the system is shut down. High performance HDDs generally require between 12-18 watts; drives designed for notebook computers are typically 2 watts.
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