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).