Advanced Micro Devices (AMD) took another step forward in its antitrust suit against Intel on Thursday by filing a subpoena in US courts for documents held by Microsoft.

AMD has charged that Intel uses its overwhelming 86 per cent market share in the microprocessor market to intimidate computer makers and retailers from buying AMD chips by threatening to withhold illegal rebates.

To prove its case, AMD has been trying to obtain documents from 32 companies that do business with Intel, including computer makers like HP and Dell, and retailers like Best Buy and Circuit City. Many agreed to supply documents when they received a subpoena, while others are resisting in court.

A Microsoft spokesperson said the company planned to comply: "Microsoft is not a party to this lawsuit, but we anticipate that both sides will be seeking documents and other evidence from Microsoft and many other participants in the PC industry. We will work with the parties in this case to respond to reasonable requests for documents and information," said Microsoft spokeswoman Lauren Irving.

Intel was not immediately available to comment for this story.

According to court documents, AMD is seeking information relating to 64-bit microprocessors, product comparisons between Intel and AMD, and any discussion of marketing arrangements involving the three companies.

The subpoena sought the same kind of documents that AMD had already requested from other companies, said AMD spokesman Michael Silverman.

AMD alleges that Intel has maintained a monopoly in the x86 microprocessor market by using exclusionary business tactics that prevent its customers from dealing with AMD.