A desktop or tower case is required to hold all your components together. It is your personal preference on which one you decide to choose. The desktop or tower cases come in two form factor, AT and ATX. Nearly all the cases made nowadays are ATX as the motherboard manufacturers make majority of their motherboard in the ATX form. All cases come with PSU (Power Supply Unit), space to mount your FDD, CD-ROM, HDD etc. The case that I would be using for the demonstration is an ATX Midi Tower case as shown below.