The European Commission started two antitrust investigations on Monday against the American computer company International Business Machines Corporation, saying that I.B.M. might have abused its dominant position on the mainframe computer market.

One investigation followed complaints by T3 and Turbo Hercules, emulator software vendors, against I.B.M.’s practices, and focuses on claims that the computer giant has tied its mainframe hardware to its dominant mainframe operating system.

According to the complaints, linking that products shuts out providers of emulation technology, which enable the users to run applications on non-I.B.M. hardware.

The second inquiry, opened on the European Commission’s own initiative, concerns claims of discriminatory behavior toward competing suppliers of mainframe maintenance services.

“The commission has concerns that I.B.M. may have engaged in anti-competitive practices with a view to foreclosing the market for maintenance services..., in particular by restricting or delaying access to spare parts for which I.B.M. is the only source,” the European Union’s executive arm said in a statement.

Mainframes are powerful computers that are used by many large companies and government institutions worldwide to store and process critical business information, with the vast majority of corporate data worldwide residing on mainframes.

In 2009 about 8.5 billion euros ($10.97 billion) worldwide and 3 billion euros in the European Economic Area were spent on new mainframe hardware and operating systems.