This is usually for new products. Items marked as educational can be purchased only using a valid student identification card. This allows you to designate what kind it is. Products that don't specify whether external or internal, you are not given the option. For instance, all Printers are external, so no need to specify.
External devices are easier to move around and switch from one computer to another.
A FPU is special circuitry in a more general microprocessor that have a special set of instructions that focus entirely on large mathematical operations. They are used extensively in 3D applications. The bus within a microprocessor that connects the CPU with main memory. It's used to communicate between the motherboard and other components in a computer system. This means that the product is included in the price of a system.