Storage Drives -- hard drives and solid state drives -- are the permanent memory for the programs and documents on your computer.
Data Transfer Rate is the rate at which data can be sent or received. This is determined by your motherboard. A drive with a higher transfer rate will only run at the rate of the motherboard's transfer rate.
Cache is a type of working memory that allows the drive to perform faster.
RPM is the rotations per minute of a hard drive which effects the speed of data transfer.
Solid State Drives are non-moving memory, so access speed is instant.
SSD Install Guide for your:
iMac 3.6GHz Intel Core i5 (27-inch - DDR3) Mid 2010