Always prioritize the official Siemens Industry Online Support (SIOS) portal. While Siemens eventually moves older versions to "legacy" status, they often provide trial versions or updates for registered users.
Windows XP SP3 or Windows 7 (32-bit) is recommended. Tia Portal 10.5 Sp2 Extra Quality Download
"Extra Quality" usually refers to a clean rip of the original installation media. Ensure your download includes the MD5 or SHA-1 checksums to verify that the file hasn't been tampered with or corrupted during the download. Tia Portal 10.5 Sp2 Extra Quality Download