The Apple II, introduced in 1977, was the machine that made Apple a major company and helped bring ready-made personal computers to the mass market. The Apple II Reference Manual, published by Apple Computer in January 1978, documents the machine in four parts: getting started with the Apple II, Apple II Integer BASIC, the Apple II firmware, and the Apple II hardware with its schematics and memory maps. Unlike the Apple I, it shipped as a complete consumer product in a molded plastic case with a built-in keyboard.
Technically the Apple II was a refined 6502 system built by Steve Wozniak. The reference manual centers on the 6502 processor and on a BASIC interpreter held in firmware so the machine was ready to program the moment it was switched on. Wozniak engineered color graphics that were generated from the same memory the processor used, a characteristically economical trick that gave the machine color and sound without expensive extra hardware.
The feature that made the Apple II endure was its openness. The reference manual documents a row of internal expansion slots that let outside companies build add-in cards, from disk controllers to memory and interface boards, turning the Apple II into a platform rather than a closed appliance. Wozniak’s later floppy disk controller plugged into this architecture and gave the machine fast, inexpensive disk storage, greatly extending what it could do.
That openness drew software, and one program in particular turned the Apple II into a business tool. VisiCalc, the first electronic spreadsheet, ran on the Apple II and gave buyers a concrete reason to spend money on a personal computer, driving sales into offices and homes alike. The combination of an affordable, expandable machine and a must-have application created the template for the personal computer market that followed.
The Apple II’s importance is that it was one of the first truly mass-market personal computers, sold for years and across many models, and that it defined the home and small-business computer as a real product category. Alongside the Commodore PET and the TRS-80, it was part of the wave of 1977 machines that put computing into ordinary hands.