The world's largest computer maker has announced plans to sell computers equipped with the open-source Linux operating system.
The gloves come off as Linux enters the ring
HP will ship the desktop computers to China, India and other Asian countries later this year.
The computers will only be sold to companies, but this could make Linux popular among private PC users as well.
HP's move poses a threat to the dominance of Microsoft's Windows operating system.
The Linux operating system offers productivity software similar to that bundled with Microsoft Windows, according to the Linux supplier Turbolinux.
IBM already uses Linux on 10,000 computers in its offices
It is already used in computer servers sold to companies by HP and its competitors Dell and IBM.
As yet, only 3% of the world's personal computers (PCs) use Linux, compared with 94% using Windows.
But Linux is boosting its market share, largely thanks to the backing of giant computer makers.
Big Blue backing
IBM is already using Linux on more than 10,000 desktop computers in its own offices.
The shift from Windows came after IBM's chief information officer Bob Greenberg last autumn challenged employees to make the switch.
Russel Coombes, HP's Linux business manager in the UK, said the company was responding to growing demand for Linux-based products in Asia.
"It just so happens that in this specific region, Linux is increasingly becoming an area where there is significant demand," he told the BBC's World Business Report (WBR).
He added that part of Linux's appeal was its lower cost.
"Cost is increasingly the biggest driver where we're seeing customers move to Linux environments."
Rupert Goodwins, editor of IT publication ZD Net, said that while Linux remained too complex for most home users, its growing foothold in the workplace would help it gain widespread popularity as soon as more user-friendly versions were developed.
"One of the things that has pushed Microsoft into the home has been that people spend a lot of time on Microsoft software in the office and feel comfortable with it when they get home," he told WBR.
"Microsoft should be very worried."
The Linux challenge is particularly effective in Asia, said Jupiter Research senior analyst Joe Wilcox.
"Microsoft hasn't really adjusted its pricing model for foreign markets, so you might pay the same price for Windows in the United States as in many other countries," he said.
"But considering the economics of some of these Asian countries, that pricing model might not make sense."
Linux is "emerging as the de facto standard" in some Asian countries, said Jim Stallings, general manager of Linux for IBM.