Why does installing a game/program sometimes take several hours, but uninstalling usually take no more than a few minutes?
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A hard drive physically stores data in a physical state (for instance, magnetic domains on a hard disk). Writing data means changing the physical state of the hard drive. Deleting data usually means just ignoring the data that is there, and forgetting how to read it.
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Let’s say we install a program that needs 8 gigabits of space.
When installing something, a little magnetic pin needs to painstakingly go to about 8 billion tiny sections of the harddrive, and make sure that it is set to “1” or “0”.
Then, a little note is made to say where on the disc the program is located, so that we can open it and make use of that program, and know not to over-write that region of the disk because it is already being used.
Later on, we decide to delete the program. We don’t actually need to change those 8 billion spots on the hard-drive.
We *could* set them all to “0” (or “1”) if we are paranoid about security, and want it to be harder to recover the deleted data.
However, we can simply have the computer delete the little note that says that space on the disc is storing this program.
Without that note, the computer forgets how to read that program, as it no longer knows where it is or how large it was. It now believes that it is safe to write over that part of the disc (which is fine by us, because if/when it writes over that part of the disc, it will be writing over some data we don’t care about, and can’t use).
Downloading and installing is building a complex lego build from instructions you found online.
Uninstalling is taking that entire lego build and throwing it into the lego box. Once it is in the lego box, all of the chunks are still there, but split up a bit and ready to be broken up for your next build.
If installing a program is like building a house, uninstalling a program is like driving over to the house and slapping a sign on it that says “condemned, land for sale.”
Your computer doesn’t waste time actually taking anything apart until it needs to use it. It just marks the house as no longer useful and then overwrites it later when it needs that land (disk space).
EDIT: this is why it’s sometimes possible to recover deleted files with a recovery program: they get marked as deleted, but they’re still there. A program that knows what to look for can find “deleted” data that hasn’t been overwritten by new data yet, and just take the “deleted” sign down.
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