Apple III Plus

The Apple III Plus was the final revision of Apple’s business-oriented Apple III line, introduced in December 1983. It featured improved reliability, a built-in clock, and a standard 256 KB of RAM, but was discontinued just a few months later in April 1984.

Apple III Plus

Apple III Plus
Specifications
Manufacturer	Apple Computer, Inc.
Type	Business Personal Computer
Released	December 1983
Discontinued	April 1984
Intro price	US$2,995 (1983)
CPU	Synertek 6502B @ 2 MHz
Memory	256 KB RAM (expandable to 512 KB)
Storage	5.25" floppy disk drive (built-in), external ProFile hard disk (optional)
Display	24 lines × 80 columns text; 560×192 monochrome graphics
Sound	1-bit beeper
Dimensions	12" × 17" × 5" (30.5 × 43.2 × 12.7 cm)
Weight	24 lb (10.9 kg)
OS / Firmware	Apple SOS, Apple III Business BASIC, Apple II emulation mode
Predecessor	Apple III
Codename	Mark Twain
Model no.	A3S2-1200, A3S2-1200A

Architecture and Processor

The Apple III Plus was powered by a Synertek 6502B microprocessor running at 2 MHz, offering double the clock speed of the original Apple II series. The system architecture was designed for business applications, with support for advanced operating systems and hardware expandability.

Key architectural features:

• 8-bit 6502B CPU @ 2 MHz
• Custom logic for memory management and peripheral support
• Apple II emulation mode via software for compatibility

Memory and Storage

The Apple III Plus shipped with:

• 256 KB RAM as standard, expandable to 512 KB via internal sockets
• Built-in 5.25" floppy disk drive (140 KB per disk, single-sided)
• Support for external ProFile hard disk drives (5 MB or 10 MB, optional)
• ROM containing Apple III firmware and Apple II emulation routines

The increased base RAM and improved memory management addressed many of the reliability issues of its predecessor.

Display and Graphics

The Apple III Plus supported:

• Text modes: 24 lines × 80 columns (business standard), 24×40 mode for Apple II compatibility
• Graphics modes: 560×192 pixels (monochrome), 280×192 (colour via Apple II emulation)
• Character generator ROM for text display
• Composite video output for monitors

These capabilities made the Apple III Plus suitable for business applications requiring high-resolution text and basic graphics.

Sound Capabilities

Sound on the Apple III Plus was limited to a simple 1-bit beeper, similar to the Apple II series. This was primarily used for system alerts and basic audio feedback.

Input/Output and Expansion

The Apple III Plus featured a range of I/O and expansion options:

• RS-232C serial port for printers and modems
• Parallel port (via optional card)
• Two Apple II–style internal expansion slots
• External floppy and hard disk interfaces
• Composite video output
• Keyboard and built-in numeric keypad
• Apple II emulation mode for running a wide range of Apple II software

These features allowed the Apple III Plus to serve both as a business workstation and as a bridge for users migrating from the Apple II.

Gallery

• 
  Front view of the Apple III Plus
• 
  Rear panel with I/O ports
• 
  Apple III Plus logic board open case