CDF way to Grid

The CDFII (Collider Detector at Fermilab II) experiment is taking data since 2001 using a multipurpose detector. Currently about 5 fb(-1) of data has been written to tape and successfully analyzed by physicists using CDF computing infrastructure. The computing architecture has evolved from the initial dedicated farms to using decentralized Grid-based resources on the EGEE Grid, Open Science Grid (OSG) and Fermilab Campus Grid. In order to deliver high quality physics results in a timely manner to a running experiment, CDF had to adapt to Grid with minimum impact on the physicists analyzing the data. The use of portals to access the computing resources has allowed CDF to migrate to Grid computing without changing how the users work. The infrastructure modifications were done by small steps over several years to reach the current stable configuration. The evolution of the architecture and the performances reached by using portals are presented here.