Canonical has not yet built an Ubuntu Linux distribution for tablets and will continue development of the OS for PCs and netbooks, company executives said.

Fast growth in tablet shipments has not affected Canonical's focus on netbooks and the company wants to push Ubuntu into more low-cost laptops, they said.

"We certainly haven't quit the netbook space -- if anything, we see growing demand for Ubuntu in PC sectors pushing into new global markets, where netbooks are the name of the game," said Mark Shuttleworth, founder of Canonical, in an e-mail response over the weekend to questions about the company's focus.

Canonical in the past has said it would build a version of Ubuntu for tablets. Some tablets, such as Kno, have shipped with Linux OSes based on Ubuntu, and many tablets with the OS have been shown at trade shows.

Canonical last week released the first beta of Ubuntu 11.04, code-named Natty Narwhal, in distinct editions for desktops, servers and netbooks. The Netbook Edition is for use only on devices using ARM processors, and its release came as a surprise as Canonical on March 9 said it would nix the Netbook Edition starting with version 11.04. The company did not release a Netbook Edition beta for the x86 architecture, integrating the code base into the Desktop Edition, which is for laptops and desktops.

ARM processors are primarily used in smartphones and tablets, and have not found success in netbook-like devices or PCs. Most netbooks ship with Intel's x86 Atom chips, but shipments of the devices are slowing down because of the popularity of tablets, according to market research firms.

The ARM-based Ubuntu 11.04 Netbook beta is not specifically for tablets, but it could be adapted for the devices, said Gerry Carr, head of platform marketing at Canonical, in an e-mail.

"We're not targeting this platform in the sense of making it available for download for people running [devices on the ARM architecture]. It's for the pre-install market only and part of our efforts to support ARM fully as an architecture. I guess you could build a tablet out of it -- but I have no idea if anyone is," Carr said.

The Ubuntu 11.04 Netbook Edition beta is designed to work with ARM-based processors including Texas Instruments' OMAP4 application processor, which is being used in Research In Motion's PlayBook tablet. The OS is based on a new user interface called Unity, which can dynamically adjust UI behavior based on screen sizes. For the ARM platform, Ubuntu is offering two separate Unity implementations, including one with advanced shaders and effects, and another with a 2D interface for lightweight devices.

More Linux-based operating systems are entering the mobile fray. Many tablets and smartphones ship with Google's Linux-based Android OS. Intel is backing the development of Meego, a Linux-based OS for smartphones and tablets, while Hewlett-Packard's proprietary webOS is based on Linux.