Integer BASIC

Integer BASIC, also called Apple BASIC, was an early BASIC interpreter created by Steve Wozniak for the Apple I and the original release of the Apple II computer.

History
After working on the video game hardware of Breakout with Steve Jobs at Atari in 1975, Wozniak started work on Game BASIC so he could write games in software without resorting to machine language. He assembled folders of papers for his BASIC design, which was based on a dialect developed for minicomputers by Hewlett-Packard, where Wozniak worked. Wozniak designed the Apple I around this implementation of BASIC, but was unable to afford a compiler at the time, so he hand assembled the instructions which he coded directly into machine language for the MOS 6502 processor.

In 1976, Apple BASIC was provided to Apple I owners on a cassette tape that took about 30 seconds to load. Because the standard configuration of the Apple I only contained 4KB of RAM, Wozniak did not have enough room to implement floating-point instructions, which he said also saved himself a few weeks' worth of development time. As games at the time mainly relied on integer functions, he implemented a small virtual machine called "Sweet 16" to support 16-bit integers. However, it was not compatible with the dialect of Microsoft BASIC that Bill Gates had based on DEC BASIC.

Apple BASIC was included directly in the ROM of the Apple II computer, released in 1977. Because scientific users requested floating-point support, Wozniak included routines that could be called from the ROMs, but did not have time to integrate them into his Apple BASIC interpreter, which he considered to be the most challenging part of designing the Apple I and II computers. Apple Computer then turned to Microsoft to adapt their version of BASIC, which supported floating-point instructions, into Applesoft BASIC.