What is IBM's biggest competitor?

Can you tell me who IBM's largest rival is in the technology sector? I'm particularly interested in knowing which company poses the most significant challenge to IBM's market share and technological advancements. Additionally, I'd like to understand what sets this competitor apart and how they might be leveraging their strengths to gain an edge over IBM. Is there a specific area of expertise or innovation where this competitor excels, and how is IBM responding to the competition?