Apple plans to upgrade its iMac today with a flashier design and thinner keyboard, according to comments and photos on industry blogs. Apple will hold a news conference today at 6pm GMT at its Cupertino, California, headquarters.

The company is expected to announce a new generation of iMac desktops with a slimmer design than the current family, which now use Intel's Core 2 Duo processors and a choice of monitors at 17in, 20in or 24in.

The new desktop line will offer only the 20-inch and 24-inch monitors, putting a greater emphasis on the visual impact of applications such as digital photos and movies, as well as the 3D graphics used in the latest video games in Microsoft's Windows Vista OS, according to postings at a number of blogs that are focused on Apple products and at more general IT blogs.

In another change, the new family of iMacs will come with a sleek keyboard, built to be much thinner than current models and use lower-profile keys, according to claimed photos published on several blogs.

Global desktop sales have been sinking in relation to notebook sales in recent years. In the second quarter, US retail desktop sales were down 10 per cent compared to the same period last year, while notebook sales rose 43 per cent over the same period, according to figures published in July by Current Analysis West. The decline pushed the share of desktops for the total US PC market down to an all-time low of 31 per cent, with notebooks holding the remaining 69 per cent.

Still, vendors can make a good profit on desktop sales, so Apple's move could be a smart way to wring revenues from that market before it shrinks even more, one analyst said.

"As far as putting effort into desktops, there is still some demand there, in most segments. Specifically, in education and the SMB space, which is where Apple focuses much of their attention," said Doug Bell, an analyst with IDC. Neither Bell nor two other analysts contacted for this story had been briefed on Apple's specific plans. Apple has a reputation for being far more secretive than other hardware vendors when it comes to briefing analysts on new products before they launch.

Upgrading the desktop line could help Apple improve its ranking in the PC market, where it is the fourth-largest vendor in the US, in a virtual tie with competitors Gateway, Toshiba and Acer, according to IDC. All four companies lag far behind market leaders HP and Dell.

The iMac upgrade would also represent a return to its roots for Apple, although the company has generated far more attention in recent years for its iPod and iPhone mobile products and iTunes. In March, Apple made a move toward another new market when it launched the Apple TV, a set-top box that can pull media content off a computer and play it on a television.