HardDisk Drive:-

Hard disk drive stores all your data including operating system, applications, user files and documents. It is a non-volatile storage, which means the contents of the HDD is not lost if the PC is switched off.

Processor CPU:-

The processor also known as CPU (Central Processing Unit) is the brain of a computer. The faster the processor, the faster it will execute instructions and run your programs. The leading Processor manufactures are Intel and AMD. Whichever manufacturer you decide to choose you will have to make sure that you purchase a compatible motherboard.

MotherBoard:-

A motherboard is a Printed Circuit Board (PCB) that connects your processor, memory and all your expansion cards together to assemble a PC. Most motherboards made nowadays are ATX. An ATX motherboard has the standard I/O (Input/Output) connectors such as PS/2 ports, USB ports, parallel port, serial port, etc, built onto the motherboard. ATX motherboard fits into a standard ATX case. The following is a picture of a Modern ATX motherboard.