Motherboard/Mainboard – This is the main circuit board that pretty much connects everything together. It will have space for a cpu or processor, memory slots for a number of sticks of memory, expansion slots, graphic slots etc. It will also have a number of connections to interface with things like keyboards, mice, usb devices, printers, serial devices etc etc. The type of external connections available vary from model to model.
Power supply – This as the name suggests is used to power the whole system.
CPU – This is the brain of a computer and come in a number of different types and socket sizes or types
Memory – Memory comes in different types and sizes and is used as temporary storage for data. This comes in static and dynamic or volatile and non-volatile.
Optical Storage – There are various types of optical storage devices inclusing cd, dvd and blu-ray.
Magnetic Storage – This is where a computer stores all its programs and data that it needs to read and write to.
Case – This is to put all the components in and come in a variety of types.