Shares of IBM are sliding before the market open on Tuesday as the company provided preliminary second-quarter results that are below Wall Street’s expectations.

CEO Arvind Krishna writes letter to investors to explain "performance shortfall"

Shares of IBM are sliding before the market open on Tuesday as the company provided preliminary second-quarter results that are below Wall Street’s expectations.

IBM shares tumbled sharply in premarket trade after the company flagged weaker-than-expected second-quarter results, missing both profit and revenue estimates. Management…