Microsoft plans to lay off about 4 percent of its work force, or 9,000 people, due to the tightening job market at big technology companies. Despite the shaky economy, Microsoft's last earnings report showed investors have driven its market valuation up to almost $3.7 trillion. However, Microsoft is in the middle of an expensive investment in A.I., including spending billions to lease and build data centers to support the demand for cloud computing and A.I. The job cuts are a sign that Microsoft’s A.I. development are having an impact on the size of its work force.