What version of OS are you running and how old is your PC? My PC is 6 years old and it came with a 2.2 TB HDD built in and the OS is Windows 10 Pro. I rarely worry about space. "Philalethes" gave you the BEST answer.
This is the best answer ever.You already have a gallon in a quart jar, you are asking if anyone knows how to rewrite the laws of physics. As far as I and the scientific community knows, it's not possible.
You already know the answers, you just don't care to hear them. 100GB hard drive? You're kidding, right? This is 2022, not 1990. The only possible solution without altering your hardware would be to move those programs to a SaS environment and run them in the cloud which essentially turns your system into a terminal and relies on the remote server to provide adequate storage and processing power. In that scenario you could get by with your tiny 100GB drive.
"best?" if the guy can't afford to buy a new drive, how is he going to afford running programs from the cloud? Esp. if he is running cracked progs? No way he can install. What then when internet goes down? Anything stored on the cloud is invitation to more privacy intrusion, and the possibility of them losing your data.This is the best answer ever.
1) Redirect the following directories to another drive or secondary partition:
There is multiple ways. Have you tried compressing all dll and exes with UPX?