Lotus 1-2-3 became the first ‘killer application’ for the IBM PC. Mitch Kapor developed Lotus 1-2-3 for the IBM PC based on word processor, spreadsheet and database. This software was a huge contributor to the success of IBM. It overtook the sales of VisiCalc and in 1995 IBM purchased Lotus. It stayed very close to the model of VisiCalc, including the “A1” letter and number cell notation, and slash-menu structure. It was cleanly programmed and relatively bug-free, gained speed from being written completely in x86 assembly language.