What is clustering? Advantages?

What is clustering? Advantages?
Sol:
A configuration that may provide better performance with multiple processors
You will notice in this graphic a cluster (or group of server processes) residing on the same physical machine.
Vertical scaling is defining multiple members of the same cluster on the same physical machine. Other components such as the Web server and deployment manager can be on the same machine or on separate machines. Vertical scaling is appropriate in environments with large, under-used machines.
A single Application Server runs in a single JVM process, and cannot always fully utilize the CPU power of a large machine and drive the load up to 85 - 100%. This is particularly true on large multiprocessor machines, because of inherent concurrency limitations within a single Java Virtual Machine (JVM). Vertical scaling provides a straightforward mechanism to create multiple JVM processes, which together can fully utilize all the processing power available.
How does horizontal scaling differ from vertical scaling?