A surgical robotic arm (520) for use with an external vision system (512) includes onboard control and at least four degrees of articulation. The robotic arm (520) can position various tools (534) in the surgical theatre responsive to positional feedback from the vision system (512). Exemplary tools (534) include a handpiece (519) that includes a motorized burr or saw, a cutting guide (542) for a handheld saw, and a laser to actively define a resection area for a surgeon. The tool (534) or a reference point on the arm (520) relative to the tool (534) includes fiducial marks to register the position of the tool (534) with the vision system (512). Exemplary tools (534) are especially suited for knee and hip arthroplasty and can be moved under processor or manual control.