A PowerBook G5 isn't ready for market yet, Apple said yesterday.

Speaking to Cnet News.com, Apple's vice president of product marketing, Greg Joswiak, said: "The challenges of cooling a G5 in a PowerBook are significantly greater."

Power and heat dissipation has been a major challenge for Apple as it utilised IBM's new PowerPC 970 and 970FX processors, leading the company to employ a complex cooling system in its PowerMac and Xserve lines.

The new G5 iMac employs a highly-designed but complex cooling system of its own. It has an air intake hole just near the speakers and integrates three fans.

Speaking in November 2003, Apple's director of product marketing for portables and wireless Dave Russell warned it "would be a while" until Apple delivers a PowerBook G5. Apple has previously pointed-out that it took the company three years to achieve a G4 PowerBook.