If the main Cadence site is slow, use their public software portal:
🔗 https://www.cadence.com/en_US/home/support/downloads.html
Then search for “Allegro Free Physical Viewer 17.4”
Version numbers matter immensely in EDA software. Allegro 17.2 and earlier used a different database structure. Starting with 17.4, Cadence introduced a new database revision (also known as "Allegro 17.4-2019"). A viewer from 16.6 or 17.2 cannot open a 17.4 .brd file. If your colleagues or suppliers are sending you 17.4 designs, you have no choice but to find the 17.4 viewer. allegro free physical viewer 174 download link
Direct Link Note: Cadence does not allow the public distribution of direct hotlinks to their .exe files because they change with every hotfix release (S001, S002, etc.). If you see a website offering a static "Click here to download 174.exe" link, it is likely outdated or malicious. If the main Cadence site is slow, use