By increasing the speed do you mean data or system?
The fundamental principle behind RAID is the use of multiple hard disk drives in an array that behaves in most respects like a single large, fast one. There are a number of ways that this can be done, depending on the needs of the application, but in every case the use of multiple drives allows the resulting storage subsystem to exceed the capacity, data security, and performance of the drives that make up the system, to one extent or another. The tradeoffs--remember, there's no free lunch--are usually in cost and complexity.
Jargon explained: clock, megahertz/gigahertz, cycle
Computer performance is a traffic problem, moving data and instructions from memory and around inside the chip. Most people think of "traffic" in terms of cars and highways. However, there is a more relevant traffic analogy that everyone experienced before they learned to drive.
To increase Data transfer to memory you will need to set up a RAID. This is a system of splitting Data across HDD. RAID 0 and 1 are the most popular.
System speed is dictated by many more variables.
Each subject should be approached separately as both are equally confusing.