VisiCalc (for "visible calculator") was the first spreadsheet computer program for personal computers, originally released for Apple II by VisiCorp on 17 October 1979. It is often considered the application that turned the microcomputer from a hobby for computer enthusiasts into a serious business tool, prompting IBM to introduce the IBM PC two years later. VisiCalc is considered to have been Apple II's killer app. It sold over 700,000 copies in six years, and as many as 1 million copies over its history. Initially developed for the Apple II computer using a 6502 assembler running on the Multics time sharing system, VisiCalc was ported to numerous platforms, both 8-bit and some of the early 16-bit systems. In order to do this, the company developed porting platforms that produced bug compatible versions. The company took the same approach when the IBM PC was launched, producing a product that was essentially identical to the original 8-bit Apple II version. Sales were initially brisk, with about 300,000 copies sold. VisiCalc used the A1 notation in formulas. When Lotus 1-2-3 was launched in 1983, taking full advantage of the expanded memory and screen of the PC, VisiCalc sales ended almost overnight. Sales declined so rapidly, that the company was soon insolvent. Lotus Development purchased the company in 1985, and immediately ended sales of VisiCalc and the company's other products. History Dan Bricklin conceived VisiCalc while watching a presentation at Harvard Business School. The professor was creating a financial model on a blackboard that was ruled with vertical and horizontal lines (resembling accounting paper) to create a table, and he wrote formulas and data into the cells. When the professor found an error or wanted to change a parameter, he had to erase and rewrite several sequential entries in the table. Bricklin realized that he could replicate the process on a computer using an "electronic spreadsheet" to view results of underlying formulae. Bob Frankston joined Bricklin at 231 Broadway, Arlington, Massachusetts, and the pair formed the Software Arts company, and developed the VisiCalc program in two months during the winter of 1978–79. Bricklin wrote: with the years of experience we had at the time we created VisiCalc, we were familiar with many row/column financial programs. In fact, Bob had worked since the 1960s at Interactive Data Corporation, a major timesharing utility that was used for some of them and I was exposed to some at