Remove the three (or on some models, four) T8 security Torx screws on the underside of the PS3 slim.

What's that, you say? Security screws? Yes, that's right. These screws have a pin in the center of them that prevents an ordinary Torx screwdriver from working. These screwdrivers are widely available, just not quite as easy to come by as a normal Torx.

Sony did this to prevent people like us from taking it apart.

Those three T8 security Torx screws seem to be the only non-Phillips head fasteners on the entire device.