It contains the processing device.
inpuit
Technically it's neither as it's just a shell that houses the devices. However, if you just mean the computer as a whole, then it is of course both because it's made up of input and output devices.
The "tower" part of a computer contains most of the computer. It is the cabinet that contains input and output devices, as well as storage devices. However, collectively speaking, the label of "processing device" would be more accurate. Or you can say it is an I/O and processing device with storage.
A computer is an output device.
Define the output device in computer?
The result of a computer's processing is known as "output."
Output is like, if you print something, the information on the paper is output. If you are listening to music on the computer, the sound is output. If you are watching a movie, the actions, the images, and the sound is output. In other words, output is something the computer provides for you.
The computer output is what one will see on a screen. For example the image text can be seen on ones computer would be considered output. There is also audio output which is what one hears through computer speakers.
Input
output
The output of a computer can be purely visual, in which case the output device is a monitor, or it can be printed, in which case the output device is a printer; when computers produce sound, the output device is a speaker.
Your tower is your computer. If you are asking if the monitor and computer have to match the answer is no. You can use any monitor with any computer.