Dell:

Dell has been attempting to offset its declining PC business, which still accounted for half of its revenue and generates steady cash flow, by expanding into the enterprise market with servers, networking, software, and services. It avoided many of the acquisition writedowns and management turnover that plagued its chief rival Hewlett Packard. Dell also managed some success in taking advantage of its high-touch direct sales heritage to establish close relationships and design solutions for clients. Despite spending $13 billion on acquisitions to diversify its portfolio beyond hardware, the company was unable to convince the market that it could thrive or made the transformation in the post-PC world, as it suffered continued declines in revenue and share price. Dell's market share in the corporate segment was previously a "moat" against rivals but this has no longer been the case as sales and profits have fallen precipitously.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who was Dell's main business rival?
Hewlett Packard