The Philips CDM9 Pro was the last Philips single-beam CD drive mechanism. Thereafter, they switched to the 3-beam linear tracking system adopted early on by Japanese manufactures. Philips chose a linear tracking construction that moved the optical lens block in a straight line because computer CD-ROM drives requiring high read speeds were in demand.
The swing arm system using a counter-weight had too much moving mass and too slow random access times for this application. In addition, because the swing arm system used in tracking error angle, it was not possible to use this system with more than a single-beam. For high-speed reading, a 3-beam system that can pick up adjacent pit streams is more advantageous.
Single-beam swing arm type drive mechanisms however are sufficient for audio only systems that do not require high speed operation.