Three rivals of IBM have dropped a major European Commission antitrust complaint against the supplier, around mainframe technology.

T3 Technologies, Neon Enterprise Software and Turbo Hercules have all withdrawn their complaint that IBM had illegally tied its mainframe hardware to its operating system, preventing customers from choosing alternatives when they bought one IBM product.

The complaints had prompted an EC investigation, which may still go ahead but is understood to be significantly weakened by the news.

The EC had made little headway in its investigation, the Financial Times reported, but US regulators continue to assess competition in the market place. An EU mainframe maintenance services probe also remains.

IBM initially reacted forcefully to the complaints, the FT noted, partly blaming Microsoft - which had invested in two of the companies that were making the complaints.