Real time error checking is required in optical disk systems to improve data reliability and to increase data throughput to/from the computer. This paper describes a two-beam optical head which meets the requirement. The head is composed of two laser diodes (830 nm for write and servo operations, 780 nm for read operation), dichroic mirrors, and an achromatic objective lens. New optical servo technologies have been developed and incorporated in this optical head. One is a new focusing technology (called the Wax-wane method) which needs only two optical components. Another is a new tracking technology (called the ILT method) which enables a tracking range of ±400 μm.