The Mega II is a custom

chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genom ...

from

Apple Computer Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

that is essentially an entire

Apple II The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-m ...

computer-on-a-chip. At least three products from Apple made use of the chip between 1986 and 1995. It was most predominantly used in the

Apple IIGS The Apple IIGS (styled as II), the fifth and most powerful of the Apple II family, is a 16-bit personal computer produced by Apple Computer. While featuring the Macintosh look and feel, and resolution and color similar to the Amiga and Atari ST ...

microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PC ...

, and the basis for a modified variant, called the "Gemini" chip, which was later used in the Apple IIe Card for the

Macintosh LC The Macintosh LC is a personal computer designed, manufactured, and sold by Apple Computer, Inc. from October 1990 to March 1992. Overview The first in the Macintosh LC family, the LC was introduced with the Macintosh Classic (a repackaging o ...

. This custom

application-specific integrated circuit An application-specific integrated circuit (ASIC ) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficie ...

(ASIC) integrated most of the circuitry from earlier Apple II models onto one 84-pin PLCC

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

, drastically simplifying design and cost for Apple. The Mega II contained the functional equivalent of an entire Apple IIe computer (sans processor), which, combined with the

65C02 The Western Design Center (WDC) 65C02 microprocessor is an enhanced CMOS version of the popular nMOS-based 8-bit MOS Technology 6502. The 65C02 fixed several problems in the original 6502 and added some new instructions, but its main feature ...

processor, plus ROM and RAM, provided full support for legacy (8-bit) Apple II software in the Macintosh LC. The result was one of the earliest single chip examples of full system

hardware emulation In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware (typically a system under design) with another piece of hardware, typically a special purpose emulation system. The emu ...

. The Mega II has the built-in equivalent of the IOU and

memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical ad ...

(MMU) chips, video and keyboard

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...

s (with support for other display languages) and likely the keyboard encoder found in the IIe. It also has a built-in keyboard and mouse controller (neither were used in the Apple IIGS). Potentially the Mega II could have been used to produce future models of the 8-bit Apple II with a very low chip count (and reduced physical size) but instead used for IIe emulation on the Apple IIGS and Macintosh LC with plug-in card. It was also used as support circuitry on the Apple II Video Overlay Card.

History

In 1984, after the cancellation of the Apple IIx project, Dan Hillman and Jay Rickard, engineers at Apple, were assigned to lower the cost of the Apple II. They were able to compress the design of almost the entire Apple II onto one chip which they named Mega II.Apple II History, Chapter 10 - The Apple IIGS
/ref> When the

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

Apple IIGS project came onto the table, the virtually completed design of the Mega II was a clear starting point for seamless backwards

8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...

system compatibility.

References

{{Reflist Apple II family