A surgical robotic manipulator system comprising: a movable surgical instrument holder; a surgical instrument mountable to the surgical instrument holder, the surgical instrument comprising an end effector; a proximal base; and an arm assembly pivotally coupled to the proximal base at a driven first pivotal joint and pivotally coupled to the instrument holder, wherein the arm assembly includes: a first link having a longitudinal first axis, a second link having a longitudinal second axis, a driven pivotal arm joint coupling the first link to the second link to vary an angle between the longitudinal first axis and the longitudinal second axis around a pivotal axis, a driven first roll joint between the base and pivotal arm joint, wherein the first roll joint has a first roll axis extending along the longitudinal first axis, a driven second pivotal joint between the first roll joint and the first pivotal joint, a third link having a longitudinal third axis, the third link extending between the first pivotal joint and the second pivotal joint, and a fourth link having a longitudinal fourth axis, the fourth link extending between the second pivotal joint and the first roll joint, wherein the arm assembly is configured such that the first roll joint provides an additional degree of freedom of the arm assembly that allows additional poses or configurations of the arm assembly for a given end effector position that allow the arm assembly to avoid obstacles, avoid collisions, avoid joint limits, and/or avoid singularities. a movable surgical instrument holder; a surgical instrument mountable to the surgical instrument holder, the surgical instrument comprising an end effector; a proximal base; and an arm assembly pivotally coupled to the proximal base at a driven first pivotal joint and pivotally coupled to the instrument holder, wherein the arm assembly includes: a first link having a longitudinal first axis, a second link having a longitudinal second axis, a driven pivotal arm joint coupling the first link to the second link to vary an angle between the longitudinal first axis and the longitudinal second axis around a pivotal axis, a driven first roll joint between the base and pivotal arm joint, wherein the first roll joint has a first roll axis extending along the longitudinal first axis, a driven second pivotal joint between the first roll joint and the first pivotal joint, a third link having a longitudinal third axis, the third link extending between the first pivotal joint and the second pivotal joint, and a fourth link having a longitudinal fourth axis, the fourth link extending between the second pivotal joint and the first roll joint, wherein the arm assembly is configured such that the first roll joint provides an additional degree of freedom of the arm assembly that allows additional poses or configurations of the arm assembly for a given end effector position that allow the arm assembly to avoid obstacles, avoid collisions, avoid joint limits, and/or avoid singularities. a first link having a longitudinal first axis, a second link having a longitudinal second axis, a driven pivotal arm joint coupling the first link to the second link to vary an angle between the longitudinal first axis and the longitudinal second axis around a pivotal axis, a driven first roll joint between the base and pivotal arm joint, wherein the first roll joint has a first roll axis extending along the longitudinal first axis, a driven second pivotal joint between the first roll joint and the first pivotal joint, a third link having a longitudinal third axis, the third link extending between the first pivotal joint and the second pivotal joint, and a fourth link having a longitudinal fourth axis, the fourth link extending between the second pivotal joint and the first roll joint, wherein the arm assembly is configured such that the first roll joint provides an additional degree of freedom of the arm assembly that allows additional poses or configurations of the arm assembly for a given end effector position that allow the arm assembly to avoid obstacles, avoid collisions, avoid joint limits, and/or avoid singularities.