The Personal System/2 or PS/2 was a line of personal computers developed by International Business Machines Corporation (IBM). Released in 1987, the PS/2 represented IBM's second generation of personal computer following the original IBM PC series, which was retired following IBM's announcement of the PS/2 in April 1987. Most PS/2s featured the Micro Channel architecture bus—a closed standard which was IBM's attempt at recapturing control of the PC market. However some PS/2 models at the low end featured ISA buses, which IBM included with their earlier PCs and which were widely cloned due to being a mostly-open standard. Many models of PS/2 were made, which came in the form of desktops, towers, all-in-ones, portables, laptops and notebooks.