|Attribute or characteristic
||Hard disk drive
||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
||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.
||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
||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
||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)
||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.
||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
||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
||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.