release supported tape cassette storage, but that was quickly dropped. At VisiCalc's release, Personal Software promised to port the program to other computers, starting with those that used the MOS Technology 6502 microprocessor, and versions appeared for Atari 800 and Commodore PET, both of which could be done easily, because those computers used the same processor as Apple II, and large portions of code could be reused. The PET version, which contained two separate executables for 40 and 80-column models, was widely criticized for having a very small amount of worksheet space due to the developers' inclusion of their own custom DOS, which used a large amount of memory (the PET only had 32k versus Apple II's available 48k). Other ports followed for Apple III, the Zilog Z80-based Tandy TRS-80 Model I, Model II, Model III, Model 4, and Sony SMC-70. The TRS-80 Model I and Sony SMC-70 ports were the only versions of VisiCalc without copy protection. The Sony SMC-70 port was the only CP/M version. Most versions were disk-based, but the PET VisiCalc came with a ROM chip that the user had to install in one of the motherboard's expansion ROM sockets. The most important port was for the IBM PC, and VisiCalc was one of the first commercial packages available when the IBM PC shipped in 1981. It quickly became a best-seller on this platform, in spite of being severely limited in order to be compatible with the versions for the 8-bit platforms. It is estimated, that 300,000 copies were sold on the PC, bringing total sales to about 1 million copies. By 1982, VisiCalc's price had risen from $100 to $250. Several competitors appeared in the market, notably SuperCalc and Multiplan, each of which added more features and corrected deficiencies in VisiCalc, but could not overcome its market dominance. A more dramatic change occurred with the 1983 launch of Lotus Development Corporation's Lotus 1-2-3, created by former Personal Software/VisiCorp employee Mitch Kapor, who had written VisiTrend and VisiPlot. Unlike the PC version of VisiCalc, 1-2-3 was written to take full advantage of the PC's increased memory, screen and performance. Yet it was designed to be as compatible as possible with VisiCalc, including the menu structure, to allow VisiCalc users to easily migrate to 1-2-3. 1-2-3 was almost immediately successful, and by 1984, InfoWorld wrote that sales of VisiCalc were "rapidly declining", stating, that it was "the