Garrys Mod Maps Install

How to install programs that are already downloaded?

Recently, my computer was reformatted and all the programs installed onto it were removed. But all the directories and files for those programs are still on my external hard drive (which was not reformatted). Even though i already have all the files, i am unable to use any of the programs themselves. I don’t want to re-download all of them, because some of them are pretty huge (such as steam and several games that i have downloaded). Also, some of them contain custom files that i spent a long time downloading (such as maps for games and models for garry’s mod).

Is there any way i can install these programs again without having to re-extract and re-download all of the files?

some programs can run without reinstalling but not all.

you really have to reinstall/re download.

how to download maps to garrys mod