# BASIC-M6502

**Repository Path**: mirrors_microsoft/BASIC-M6502

## Basic Information

- **Project Name**: BASIC-M6502
- **Description**: Microsoft BASIC for 6502 Microprocessor - Version 1.1
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: main
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2025-09-04
- **Last Updated**: 2025-09-05

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# Microsoft BASIC for 6502 Microprocessor - Version 1.1

## Historical Significance

This assembly language source code represents one of the most historically significant pieces of software from the early personal computer era. It is the complete source code for **Microsoft BASIC Version 1.1 for the 6502 microprocessor**, originally developed and copyrighted by Microsoft in 1976-1978.

### Why This Document is Historically Important

#### 1. Foundation of the Personal Computer Revolution

- This BASIC interpreter was the software foundation that powered many of the most influential early personal computers
- It democratized programming by making it accessible to non-technical users through a simple, English-like programming language
- Without this software, the personal computer revolution might have developed very differently

#### 2. Microsoft's Early Success

- This represents some of Microsoft's earliest and most successful software
- The licensing of this BASIC interpreter to multiple computer manufacturers was crucial to Microsoft's early business model
- It established Microsoft as a dominant force in personal computer software before MS-DOS or Windows

#### 3. Multi-Platform Compatibility

- This single codebase was designed to run on multiple different computer systems of the era
- The conditional compilation system allowed the same source code to target different hardware platforms
- This approach influenced how software would be developed for decades to come

## Supported Computer Systems

The source code includes conditional compilation support for multiple pioneering computer systems:

- **Apple II** (`REALIO=4`) - Steve Jobs and Steve Wozniak's revolutionary home computer
- **Commodore PET** (`REALIO=3`) - One of the first complete personal computers
- **Ohio Scientific (OSI)** (`REALIO=2`) - Popular among hobbyists and schools
- **MOS Technology KIM-1** (`REALIO=1`) - An influential single-board computer
- **PDP-10 Simulation** (`REALIO=0`) - For development and testing purposes

## Technical Specifications

- **Language**: 6502 Assembly Language
- **Target Processor**: MOS Technology 6502 8-bit microprocessor
- **Memory Footprint**: 8KB ROM version
- **Features**: Complete BASIC interpreter with floating-point arithmetic
- **Architecture**: Designed for both ROM and RAM configurations

## Key Features

### Programming Language Support

- Full BASIC language implementation
- Floating-point arithmetic
- String handling and manipulation
- Array support (both integer and string arrays)
- Mathematical functions and operators
- Input/output operations

### Memory Management

- Efficient memory utilization for 8-bit systems
- String garbage collection
- Dynamic variable storage
- Stack-based expression evaluation

### Hardware Abstraction

- Configurable I/O routines for different computer systems
- Terminal width adaptation
- Character input/output abstraction
- Optional disk storage support

## Development History

The source code includes detailed revision history showing active development:

- **July 27, 1978**: Fixed critical bugs in FOR loop variable handling and statement parsing
- **July 1, 1978**: Memory optimization and garbage collection improvements  
- **March 9, 1978**: Enhanced string function capabilities
- **February 25, 1978**: Input flag corrections and numeric precision improvements
- **February 11, 1978**: Reserved word parsing enhancements
- **January 24, 1978**: User-defined function improvements

## Cultural Impact

### Educational Influence

- This BASIC interpreter introduced millions of people to computer programming
- It was the first programming language for countless programmers who later became industry leaders
- The simple, interactive nature of BASIC made computers approachable for non-technical users

### Industry Standardization

- Microsoft's BASIC became the de facto standard for personal computer programming
- The design patterns and conventions established here influenced later programming languages and development tools
- The multi-platform approach pioneered techniques still used in modern software development

### Business Model Innovation

- The licensing of this software to multiple hardware manufacturers created Microsoft's early business model
- It demonstrated the viability of software as a standalone business, separate from hardware
- This approach became the template for the entire software industry

## Technical Innovation

### Compiler Technology

- Advanced macro system for code generation
- Sophisticated conditional compilation for multi-platform support
- Efficient symbol table management
- Optimized code generation for memory-constrained systems

### Runtime System

- Stack-based expression evaluator
- Dynamic memory management
- Real-time garbage collection
- Interactive command processing

## Legacy

This source code represents the foundation upon which the modern software industry was built. The techniques, patterns, and business models pioneered in this BASIC interpreter directly influenced:

- The development of MS-DOS and subsequent Microsoft operating systems
- The standardization of programming language implementations
- The establishment of software licensing as a business model
- The democratization of computer programming

## File Information

- **Filename**: `m6502.asm`
- **Lines of Code**: 6,955 lines
- **Copyright**: Microsoft Corporation, 1976-1978
- **Version**: 1.1
- **Assembly Format**: Compatible with period assemblers for 6502 development

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*This document represents a crucial piece of computing history - the source code that helped launch the personal computer revolution and established Microsoft as a software industry leader.*