This is just a short information about the different between Solid State Disk and Mechanical Hard Disk/Drive.
I will explain with picture. Picture below is a Solid State Disk (SSD) from SanDisk. As you can see from the picture below, SSD has no mechanical/moving parts. It simply contains memory/flash chip. Imagine a bigger USB Flash Disk, yes, SSD is simply a bigger USB Flash Disk.
Below is a standard Hard Disk Drive (HDD). It contains some platters with head that will read data from the platters. This head will move above the platters to read/write data.
SSD will be faster in random access since it has lower seek time (HDD will have to move the head above the platter in order to search data, while SSD doesn’t have to move anything).
In other side, HDD will be faster in sequential access. Its speed will be higher when reading/writing sequential data (the head don’t have to seek data, just write/read in sequentially).
In the factor of power consumption, SSD will consume less power.
In the factor of price per MB, HDD will be cheaper.
Since SSD has no moving parts, the it’s safer to be used in mobile platform (has better shock resistance). Even if you drop your SSD, the data inside – most likely – should be kept safe. While for HDD, never drop it or – most likely – you will destroy the data inside.