For educational purposes, the trial version is acceptable. For production environments, a valid license is mandatory. If you have an existing license for a newer version of TIA Portal, this license may activate V12 due to downward compatibility. However, it is always best to verify this with Siemens support or your distributor. Engineers have reported that "the professional edition also includes the functions of SIMATIC STEP 7 Basic V12," meaning a Professional license often covers the basic functionality of older versions.
Windows 7 (32-bit or 64-bit) Professional, Enterprise, or Ultimate. Windows XP SP3 is supported by some basic packages, but Windows 7 is highly recommended. Processor: Intel Core i3 or higher (or equivalent). download tia portal v12 sp1 top
From the SIOS legacy portal, download the following files (total size ~12 GB): For educational purposes, the trial version is acceptable