I found this a while ago and is why I thought more than 1 laser pickup is use now.
Multi-beam CD-ROM Drives
A new technological development, the multi-beam CD-ROM drive uses 7 laser beams instead of one to to produce 36X performance from a 6X rotation speed. Six beams are used for reading data; the other one is used for error correction. A new development by Hi-Val in multi-beam CD-ROM drives, the first 40X drive, utilize 7 laser beams, reading simultaneously. (6 that read, and one for error correction, the same as above). The yield is true 40X performance and a transfer rate that can reach 6MB/second. The CD-ROM disc rotates as smoothly as a 6X drive.