The company hopes that the new model, with increased memory and an improved graphics chip, will help it continue its revival of the past year.

After years of decline, the launch of iMac last year had seen it regain visibility and mass market credibility.

But despite continuing healthy orders a shortage of chips led Apple to warn last month that its recent profits have been hit by not having enough computers available for sale.

At the launch on Tuesday in California, chief executive Steve Jobs said Apple had received "tons of orders" for its iBook portable and production was "back on track" after some delays from the Taiwan earthquake.

Compuserve tie-up

Apple has shipped over two million iMacs in the 13 months since its launch, generating $2.2bn in revenues for the company, said Mr Jobs.

He added that company research indicates that one in three iMac purchasers are first time computer buyers, and nine out of ten are internet users.

In a separate tie-up in the US, there will be a $400 (£240) rebate to purchasers who sign up with Compuserve for Internet access.

Apple's new Mac OS 9 operating system has features to update software automatically over the internet. It also allows several users to use the same Macintosh computer while protecting private files or maintaining Internet settings.

The new iMacs feature iMovie software that allows users to create home videos by rearranging video clips and adding special effects, scrolling titles and music.

Shares rise

The movies can be saved on iMac's hard drive and downloaded to a videocam recorder to make digital or VHS-format copies.

Mr Jobs said the iMac will now have a standard 64 megabytes in memory from 32 megabytes previously and will incorporate a design feature to make it easier to upgrade memory to a maximum of 512 megabytes.

The iMac will also be compatible with the AirPort wireless ethernet card developed with Lucent Technologies that was previously only available with the iBook portable computer.

This means that once an AirPort Base Station is plugged into a phone line or cable modem iMac users can surf the Internet wirefree, as long as it is within 150 feet of the AirPort.