The pursuit of stable performance led to Philips' development of the single-beam swing arm system. Imposing a couterweight (balancing weight) on the side facing the optical lens block enables the system to adjust the weight distribution and move the optical system usigin relatively minimal power. It also facilitated increased structural precision and, perhaps even more importantly, allowed overall movement to be controlled using highly versatile analog servo circuitry. CDs are irradiated with a 780nm red laser beam from the polycarbonate resin substrate side, and whether the digital data is "0" or "1" is determined by an increase or decrease in the reflection of the laser beam. Thus, extremely accurate optical technology (lens design, lens fabrication, special coatings, and precise assembly) is required for the small optical pickup block.
As the Philips single-beam swing arm type drive mechanism evolved, the extremely compact Philips CDM4 appeared. There are many versions of the Philips CDM4, the most representative of which are the Philips CDM4M with a hard resin top plate, and the die-cast Philips CDM4MD. With the appearance of the Philips CDM4, complete miniaturization of the drive unit, including the drawer mechanism indispensable in a front-loading system, became possible.