By this time in the evolution of cognitive rehabilitation most treatment facilities have a computer-assisted cognitive retraining programme. This programme will generally be housed in the department of neuropsychology, speech and language pathology or occupational therapy. While the debate about the efficacy of computer-assisted cognitive rehabilitation (CACR) programmes continues, many persons are interested in more basic issues such as 'Which computer to buy?' While this initially may appear to be a minimum expense for a department, few people realize that the initial choice of a computer dictates the choice of software for that computer, as well as any other peripheral devices, e.g. video monitor, laser printer, or adaptive hardware equipment. This column will briefly review the three main computer operating systems which are commercially available for institutional and home markets, and discuss positive and negative attributes of each system.