SSD vs HDD

How do they work

HDD uses a writer/reader attached to a mechanical arm which moves very fast to the right location of the disk to read or write data while the platter ( where the data is stored ) spins also very fast, normally 7200  revolutions per minute. The technology in HDDs is magnetism.

SSD uses the NAND flash technology ( there is no mechanical movement involved ) which takes less time for gathering data than HDD that has to look everywhere on the disk and find the data blocks ( they may also be spread out on the disk which makes the search even slower ). SSD is just a bigger and more advanced version of a memory stick. There is a embedded processor inside SSD and it controls the data manipulation ( caching, cleaning, storing, retrieving ).



Comparison

The comparison is made on avarage.

Attribute	SSD - Solid State Drive	HDD - Hard Drive Disk
Cost per GB	$0.70	$0.1
Size - both vary	Small and lightweight	A bit heavier
Transfer speed	100 to 600 MB/s	50 to 140 MB/s
Reading latency	Very low because it happens in a flash	Has to find the data segment every time from different location
Start-up	Few milliseconds	Several seconds
Temperature	Tolerates higher temperatures. Some models even come with heat sinks.	Can get very hot in hot places or under heavy workload and may need cooling ( over 35°C / 95°F shortens lifespan ).
Reliablity	No mechanical parts. Number of times data can be erased varies between models and brands. DRAM has no "number of times" limitation. Not affected by vibration or shock.	Can fail mechanically. Possibility of data "tear". Almost no degration from workload. Strong magnetic surge can damage the stored data. Needs shock and vibration protection.
Capacity	Up to 2 TB. Most common 64-256 GB	Up to 4 TB. Most common 500 GB - 1 TB
Noise	May occur electric noise, but mainly silent.	Some but little noise.

What HDD looks like inside