With less than a week before the Apple World Wide Developers Conference kicks off, US retailers are reporting serious shortages of Mac computers, suggesting a number of refreshed models will make their debuts alongside new versions of Apple's desktop and mobile operating systems.

The computer in the shortest supply is the Mac Pro, Apple's professional workstation and in recent years its most neglected product.

It hasn't had a major update in 2010 and its loyal band of users have tried everything from bombarding Tim Cook with personal emails, to launching a Facebook campaign and publicly switching to HP and Dell computers in protest.

What's more, in Europe, it's so old that it no longer conforms with EU regulations and was withdrawn from sale in March.

Meanwhile, according to an investors note from KGI analyst Ming-Chi Kuo seen by Apple Insider, a slimmer, lighter 13-inch MacBook Pro with Retina display and a full HD front-facing FaceTime camera will also be announced.

As well as going on a diet, the entry-level Pro notebook (Apple also makes a more powerful, 15-inch MacBook Pro) will also get a chip update to Intel's new Haswell processor.

This means up to 50 percent more battery life and noticeably improved graphics.

Apple's superlight MacBook Air notebooks are also expected to get the same processors meaning that their battery life could be off the scale (they already have industry-leading battery life of over 8 hours) but Kuo is doubtful that the computers will also get Retina displays.

Otherwise, the five-day conference will be focused on software and, in particular Apple's latest changes to its OS X and iOS operating systems.

OS X is expected to get Siri integration so that the virtual assistant that made its debut on the iPhone 4S will become an integral part of its mobile and desktop computers as well as its phones and tablets.

As for iOS7, it is expected to cause shock and awe.

Shock because under Jony Ive's leadership all of the ‘cute' design elements, such as rain drops on the homescreen and yellow legal pad tinted pages in the notes app will give way to clinical, strong lines and a minimalist color palette.

And awe because a number of deficiencies, such as navigation and keyboard input are expected to have been seriously overhauled.