SAN FRANCISCO (Reuters) - Hewlett-Packard Co. (HP), the world's top PC maker, is launching a new line of inexpensive business laptops with fresh features targeting users at small and medium-size companies.

The HP ProBook s-series, which starts shipping globally yesterday, is the company's new mainstream business notebook, following the release of its higher-end, lightweight EliteBook line last year.

The ProBook replaces the HP Compaq line, although the Compaq name will continue to be used as a master brand name in other PCs.

The ProBook offers users a number of new features, including an optional Linux-based operating system pre-installed - Novell Inc.'sSuSE Linux Enterprise Desktop 11 - for those seeking an alternative to the dominant Microsoft Corp. Windows platform.

It is HP's first-ever Linux pre-install on a standard business laptop, the company said. The PC maker does offer some netbooks with Linux.

"It's pretty much a natural evolution," said Carol Hess-Nickels, HP's director of marketing for worldwide business notebooks.

"We want to provide a different option...it's probably a little time yet before we'll know exactly what the demand is, but we did think it was something worth trying."

The ProBooks come with 14-inch, 15.6-inch and 17.3-inch screen sizes, with prices starting at $529. In another first for an HP business notebook, buyers will be able to add a color finish - "merlot" - if they choose.

Some models will also feature Qualcomm Inc's Gobi technology, allowing them to use a single module to access different mobile broadband network technologies and mobile operators.

HP will also bring higher-end durability features, like its 3D DriveGuard - which protects the hard drive if a laptop is dropped - and a spill-resistant keyboard to the ProBook.

HP is the world's No.1 PC vendor, with a first-quarter global market share of more than 20 percent, according to research house IDC, well ahead of second-place Dell Inc . HP also took over the top spot in the US market from Dell in the first quarter.

The shares of Palo Alto, California-based HP closed the regular session down 35 cents at $35.45 on the New York Stock Exchange on Monday.