Apple will begin shipping its new iMac G5 desktop computer worldwide in mid-September, the company's top marketing executive said yesterday.

Philip Schiller, Apple's senior vice president of worldwide product marketing, showed off the new machine during a keynote speech at the start of the Apple Expo trade show in Paris. The screen of the new iMac is suspended above the desk like that of its predecessor, but its processor, hard disk and DVD drive are concealed behind the screen rather than in the base.

"A lot of people are going to be asking, 'Where did the rest of the computer go?'" Schiller said.

Three models will be available. The top-of-the-range model has a 20-inch LCD screen with a resolution of 1,680-x-1,050 pixels. It contains a 160GB hard disk drive, an optical drive for burning DVDs and a 1.8GHz G5 processor, and will sell for £1,148 plus VAT.

The new machines have two FireWire 400 ports, three USB ports, audio line-in, optical audio-out, video out, modem and Ethernet connections at the back of the screen. The speaker grills are concealed in the base of the screen and bounce sound off the desktop up to the user.

The other two models have 17-inch screens, 80GB hard-disk drives and optical drives that can burn CDs and read DVDs. The 1.6GHz model will sell for £782 plus VAT, and the 1.8 GHz model for £893 plus VAT.

Customers choosing the optional Wi-Fi wireless networking and Bluetooth wireless peripherals need only plug in a power cord into the back of the machine and begin surfing the Net, Schiller said.

The power button is also hidden around the back, the only raised feature on the rear surface and exactly opposite the "sleep" light on the front "so you know where to find it," Schiller said. "We like to joke that the back of our computer is more beautiful than the front of anyone else's computer."

The machines contain a Geforce FX5200 Ultra 64MB video card connected to an AGP 8x graphics bus, and can hold up to 2GB of 400MHz DDR RAM, connected via a 600MHz front-side bus. The hard drives use Serial ATA. The slot-loading optical drive is mounted vertically, top-right of the machine, with the processor bottom left, cooled by three computer-controlled fans. "We measured the iMac running," Schiller said, "and it's quieter than a whisper."

"It really is a breakthrough in personal computing," Schiller told the Apple Expo crowd. "I think that's what Apple is all about."

Schiller's presentation contained almost all the essential elements of an Apple keynote -- screening of a new TV advertisement, slick software demonstrations, and a new product rising from beneath the stage to wild applause -- but one ingredient was missing: CEO Steve Jobs, who is at home recovering from surgery.

"He's doing great, and will be back at work in September," Schiller said. "September can't come soon enough."

Jobs will be back at work just in time to play a new Mac video game based on "The Incredibles," a film produced by another company of which he is CEO: Pixar. Shiraz Akmal, director of development for the game's developer, THQ, joined Schiller on stage to demonstrate the game.

Other software showcased during the 90-minute presentation included a forthcoming rendering engine from Luxology, publisher of the 3D modelling tool Modo. Luxology President Brad Peebler showed the software prototype rendering a scene composed of 1.18 billion polygons in 37 seconds.

Apple's Motion real time moving graphics design package also put in an appearance, directed by its technical marketing manager, Joseph Linaschke. The software is now shipping, priced at around £170 plus VAT. The product is priced low because "We want to get this power into the hands of a lot of our customers," Linaschke said.

Schiller also called on a number of his colleagues to demonstrate features that will be included in the next release of Apple's Mac OS X operating system software, Tiger. It will go on sale in the first half of 2005, more than a year before Microsoft's update to its Windows operating system, Longhorn.

"I'm not sure anyone knows when Longhorn is coming, but I know this is well in advance of that," Schiller said.