The offline installer for .NET Framework 3.5 SP1 was a godsend for users with slow internet connections or those who needed to deploy the framework to multiple machines without an internet connection. This self-extracting executable file contained all the necessary files to install the .NET Framework 3.5 SP1 without requiring an active internet connection.

The installer was approximately 231 MB in size, which was still a significant size, but much more manageable than downloading the entire framework from scratch. Users could simply download the offline installer, save it to a USB drive or CD, and then install it on their machine or a machine without an internet connection.

Yes. A common misconception is that .NET Framework 4.8 replaces 3.5. They run side-by-side. Version 4.x is for modern apps; version 3.5 is for legacy apps. You need both installed simultaneously.