The IBM Convertible lap-top Personal Computer has made very little impact in the market so far as potential buyers compared it with similar machines made by the likes of Toshiba and Zenith and picked one of the clones. IBM yesterday moved to answer some of the criticisms by coming up with a new LCD screen using contrast-enhancing supertwist technology, and providing a wider viewing angle and an etched glass screen that reduces glare. The new screen is standard on all new Convertibles, and is available as an upgrade for existing users. An Enhanced Internal Modem gives Hayes command set 3 compatibility as well as the IBM standard, and new 256Kb memory board enables main store to go to 640Kb. People who buy a Convertible in the US before May 1 get a free copy of PC-DOS 3.2. The Convertible with enhanced LCD is $1,995, the new screen is $250; the Enhanced Modem is $450, and the 256Kb memory board $390.