System comprising a slide rail assembly, the slide rail assembly, comprising: a first rail having a longitudinally extending main body; a second rail having a longitudinally extending main body and slidably connected to the longitudinally extending main body of the first rail; and a ball assembly comprising a ball retainer and a plurality of balls arranged in the ball retainer, the ball assembly being movably mounted between the first rail and the second rail, the ball retainer comprising a lateral portion corresponding in position to a space between the longitudinally extending main body of the first rail and the longitudinally extending main body of the second rail; wherein the longitudinally extending main body of the second rail further comprises a projecting block for pushing the lateral portion of the ball retainer and thereby keeping the lateral portion of the ball retainer close to the longitudinally extending main body of the first rail, wherein the second rail includes an upper wall, a lower wall opposite to the upper wall, and a sidewall connected between the upper wall and the lower wall, wherein the sidewall of the second rail has at least one mounting portion, and a block member is mounted on the sidewall of the second rail, characterized in, that the system further comprises a chassis, the chassis comprises a mounting member, and that the at least one mounting portion is configured to be mounted to the mounting member provided on at least one lateral side of the chassis to be connected and fixed to the second rail of the slide rail assembly, and that the block member can be pressed against the mounting member when the mounting member is mounted at the mounting portion of the sidewall of the second rail. a first rail having a longitudinally extending main body; a second rail having a longitudinally extending main body and slidably connected to the longitudinally extending main body of the first rail; and a ball assembly comprising a ball retainer and a plurality of balls arranged in the ball retainer, the ball assembly being movably mounted between the first rail and the second rail, the ball retainer comprising a lateral portion corresponding in position to a space between the longitudinally extending main body of the first rail and the longitudinally extending main body of the second rail; wherein the longitudinally extending main body of the second rail further comprises a projecting block for pushing the lateral portion of the ball retainer and thereby keeping the lateral portion of the ball retainer close to the longitudinally extending main body of the first rail, wherein the second rail includes an upper wall, a lower wall opposite to the upper wall, and a sidewall connected between the upper wall and the lower wall, wherein the sidewall of the second rail has at least one mounting portion, and a block member is mounted on the sidewall of the second rail, characterized in, that the system further comprises a chassis, the chassis comprises a mounting member, and that the at least one mounting portion is configured to be mounted to the mounting member provided on at least one lateral side of the chassis to be connected and fixed to the second rail of the slide rail assembly, and that the block member can be pressed against the mounting member when the mounting member is mounted at the mounting portion of the sidewall of the second rail.