The Apple IIc Plus is the final model of the Apple II series produced by Apple Computer in 1988.

It has a 65C02 CPU running at 4MHz, 128KByte of RAM which was expandeable to 1.125MByte. It came with a 3.5" floppy disk drive and ran the ProDOS operating system. The machine itself was not really an upgrade to prior models, but rather integrated some of the existing peripherals of prior models into one machine. Being an 8-bit machine, it lacked in performance compared to the much more advanced 16-bit Apple II GS.

Video Modes

• 40/80 x 24 text mode
• 40/80x48 in 16 color
• 280x192 in 6 color
• 560x192 in 16 color with pixel placement restrictions

1. MIG and 2KByte SRAM
2. Internal modem connector
3. Dual 8KByte CPU cache
4. ASIC accellerator
5. 65C02 CPU @4MHz
6. Memory expansion connector

Apple DOS

Technically, Apple DOS provided three primary components: the DOS image (disk-resident routines), the File Manager, and the Program Manager. The File Manager translated high-level commands into sector-level disk operations, while the Program Manager handled loading and saving of executable binaries. Disk I/O was tightly coupled to the unique design of the Disk II controller, which relied on software timing loops instead of complex controller hardware. Because Apple DOS lacked subdirectories and advanced metadata, disks were essentially single-level volumes, limiting scalability but maximizing simplicity. Despite these constraints, Apple DOS became the foundation of Apple II software distribution for years, until it was eventually replaced by ProDOS in 1983, which introduced hierarchical directories, improved file handling, and support for larger disks.

Apple ProDOS

From a technical perspective, ProDOS reorganized the system architecture into a modular kernel with machine-language routines resident in memory, exposing a set of entry points for file, device, and memory management. It reserved high memory for itself while leaving the lower regions available as a consistent application execution environment, which improved software portability across Apple II models. ProDOS also introduced more rigorous file typing and access control flags (read, write, destroy, rename), as well as real-time clock integration when supported by hardware. Though it was less forgiving than Apple DOS in terms of compatibility quirks, ProDOS became the standard Apple II operating system throughout the mid-to-late 1980s, supporting not only floppies but also hard disks, RAM disks, and eventually 3.5-inch drives, ensuring the Apple II line remained viable in an era of expanding storage demands.

This was the direct replacement for Apple DOS 3.3 and was entirely 8-bit, designed to run on all Apple II models with a 6502 or 65C02 CPU. It introduced hierarchical directories, block-based I/O, and support for larger disks. This version remained the standard OS for 8-bit Apple II machines.

ProDOS was strictly limited to a 64 KB address space, with the kernel, file system handlers, and I/O routines resident in the upper portion of memory. Applications were constrained to what remained of conventional RAM. File buffers and directory structures were mapped into fixed RAM locations, limiting the maximum complexity of applications.

With ProDOS Apple introduced a new file system with a hierarchical directory tree, 512-byte block allocation, and 32 MB volume support. It exposed a set of machine-language entry points (the MLI, or Machine Language Interface) for file and device access. These were strictly 8-bit routines, with parameters passed through fixed memory locations.

ProDOS Served as the general-purpose disk operating system for all Apple II models (II+, IIe, IIc). It was lightweight, fit within the 64 KB space, and became the baseline for nearly all 8-bit Apple II software in the mid-1980s.

The 6502 is an 8-bit MicroProcessor designed by MOS Technology. The team was led by Chuck Peddle and had also worked on the Motorola 6800. The 6502 is a simplified, but faster and cheaper design than the 6800.

The 6502 was introduced in 1975 and was the cheapest microprocessor on the market. Together with the Zilog Z80, the 6502 helped start the home computer revolution of the 1980s. The 6502 was used in a wide range of devices: the Atari 2600, the 8-bit Atari home computers, the Apple II, the Nintendo Entertainment System, the Commodore 64, the BBC Micro and many others. All used the 6502 or a variation of it.

The 6502 is a 1MHz design, while the 6502A is designed for 2MHz. The 6502A is 100% compatible with the original 6502.

Commodore soon bought MOS Technology, but conitnued to sell the microprocessor to competitors and licensed the design to other manufacturers.