A lot of computers now days have all the main parts of the computer stored in the back of the screen, but there are still some about that still use the screen and tower units

inside workings

Inside the Tower

PSU

CD-ROM

HARD DRIVE

VIDEO CARD

RAM

CPU

FAN

MOTHERBOARD

PSU - The Power Unit

CD_ROM - (Compact Disc, read-only-memory) is an adaptation of the CD that is designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound.

HARD DRIVE - A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device that uses magnetic storage to store and retrieve digital information

VIDEO CARD - A video card is an expansion card which generates a feed of output images to a display Frequently, these are advertised as discrete or dedicated graphics cards .

RAM - Random-access memory is a form of computer data storage which stores frequently used program instructions to increase the general speed of a system.

CPU - A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program

FAN - A computer fan is any fan inside, or attached to, a computer case used for active cooling, and may refer to fans that draw cooler air into the case from the outside,

MOTHERBOARD - A motherboard is the main printed circuit board (PCB) found in general purpose microcomputers and other expandable systems.