If you are determined to play The Sims 3 on a budget and a small drive, follow this safe plan:
Step 1: Wait for a Steam sale (Summer/Winter sale). The Sims 3 base game often drops to $4.99.
Step 2: Download only the base game via Steam. Uncheck all Expansion Packs (Late Night, Ambitions, etc.). You do not need them. Sims 3 Highly Compressed 100mb Download
Step 3: Install the game to an external SD card or USB drive. Steam allows you to create a "SteamLibrary" folder on any drive.
Step 4: Install the "Sims 3 Smooth Patch" by Lazy Duchess. This patch fixes the game's famous stuttering and allows it to run better on low-RAM systems. It does not increase file size. If you are determined to play The Sims
Step 5: Turn off "Memories" and "Store Mode" in the game options. This prevents the game from bloating your save folder with 1000s of screenshots.
Final Install Size using this method: Approximately 6.2 GB. That is 62 times larger than the "100mb" myth, but it is real, safe, and will not destroy your computer. Uncheck all Expansion Packs (Late Night, Ambitions, etc
If you are looking for a 100mb file because your computer is old, your internet is slow, or your hard drive is full, you have legitimate, legal options that won't give you a virus.
While 100MB is fake, you may find legitimate "repacks" from trusted groups (like FitGirl or Masquerade) in the modding community.
In rare cases, you might find a repack that is split into parts. The "100mb" file is just Part 1 of 30. Once you download all parts, you end up with 15 GB anyway.