HDD: Hard disk drives consist of one or more magnetically sensitive platters, an actuator arm with a read/write head on it for each platter, and a motor to spin the platters and move the arms. There is also an I/O controller and firmware that tells the hardware what to do and communicates with the rest of the system.
The platters spin at preset speeds (4200 rpm to 7200 rpm for consumer computers). Those speeds correlate to read/write rates. The higher the preset speed, the faster a hard drive will be able to read and write data.
SSD (Solid State Drive)
img:Boston univ Solid-state drives use flash memory to deliver superior performance and durability. Because there are lots of small, moving parts inside your hard drive — magnetic heads, spindles, and spinning platters — it’s easy for things to go wrong and you could lose your important data. Without moving parts, SSDs are more durable, run cooler and use less energy.
WHY SSD IS BETTER THAN HHD: Solid-state drives deliver faster load times for games, applications, and movies. Because of the technology they use, SSDs are lighter and better able to withstand movement and drop page. Also, solid-state drives to use less energy, allowing computers to run cooler. SSD prices have come down a lot in recent times, too, with the price per gigabyte much lower than it once was. Large capacity drives are still expensive, as are the highest performing ones, but, they’re more affordable than ever.