As IBM releases more details of its portable micro it has become clear that the delivery of the new micro has been brought forward to fill a gap caused by poor demand for the PC Jr.

IBM says that the Portable PC will be available for demonstration and purchase in the US from March 1, but: "initial supplies will be limited".

One reason for the limited supplies could be the lack of chips (a worldwide problem for most micro makers). But IBM has taken steps to protect itself by buying shares in Intel, manufacturer of the 8088 processor chip used in the PC, Jr and Portable PC.

If sales of the Jr are below target, then switching the components to production of the portable would make sense.

This seems to be backed up by reports from America. The Jr seems to be selling well to corporate customers who want a Jr at home because of its compatibility with the machine in the office. But sales to new customers seem to be relatively thin on the ground.

Main criticisms about the Jr stem mainly from the keyboard (roundly criticised by many reviewers of the micro) and its high price. By bringing out the Portable PC ahead of schedule IBM could fill the shortfall in Jr sales while making life tougher for other manufacturers which have attempted to fill the gap in IBM's product range.

The Portable PC weighs more than some of its competitors (it's a luggable 30 lbs) and doesn't offer as full a range of facilities (although these will surely come).

The basic machine costs $2,795 and features a 9" amber monitor, 256K or RAM (expandable up to 512K RAM), a universal power supply for use in different countries, a single 360K disk drive (with a second drive available as a $425 option) and a colour graphics monitor adaptor.