Difference between revisions of "Apple IIGS emulators"

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Latest revision as of 13:36, 7 February 2021

Apple IIGS
AppleIIGSPC.png
An Apple IIGS PC.
Developer Apple Computer, Inc.
Type Computers
Release date September 1986
Discontinued December 1992
Predecessor Apple II
Emulated

The Apple IIGS is a 16-bit PC produced by Apple Computer Inc. It was created to compete with the Amiga and the Atari ST lines of PCs.

Despite the Apple IIGS name, it is a completely different architecture. The system has a chip called the “Mega II” which is an Apple //e on a chip, making it fully backwards compatible with Apple ][ software.

It was the first machine from Apple to use the Apple Desktop Bus and the first to provide a colour version of QuickDraw since the first colour Macintosh was not available until 1987. However it does not provide a high-resolution square pixel mode.

Emulators[edit]

Name Platform(s) Latest version Active Recommended
PC / x86
KEGS Windows Linux macOS 1.05
GSplus Windows Linux macOS 0.14 ~
GSport Windows Linux macOS 0.31
MAME Windows Linux macOS FreeBSD 0.230

Processor[edit]

The central processor is a 65816, a backwards-compatible 16-bit update to the 6502 that was also used in the Super Nintendo. It runs natively at 2.8Mhz but will slow down to ~1Mhz when in classic Apple II emulation mode or when writing to video memory.

Graphics Capabilities[edit]

In addition to RGB emulations of the existing Apple II artefact composite video modes, the IIgs adds 320x200 and 640x200 RGB colour modes; the former in various combinations of 16 colours per line and the latter at 4 colours per line (including a hardware dithering mode that acts a little like 16 colours per line). Each line may use any of 16 palettes, making a total of 256 colours on screen without raster-linked palette changes.

There is also some support for 'fill mode', in which colour 0 means "repeat the last non-zero colour", designed to aid in fast single-colour fills.

Colours are selected from a 12-bit RGB 4,096 colour palette; the IIGS therefore has the same total colour range as its contemporaries the Commodore Amiga, the Atari STE and the Acorn Archimedes.

However it is subject to a number of deficiencies: there is a single buffer for video only — double buffering is not supported — and it supports neither hardware scrolling nor hardware sprites; and as all writes into video memory clock the CPU down to 1Mhz these are expensive to perform in software.

Audio Capabilities[edit]

The IIGS provides a 32-channel wavetable Ensoniq sound chip, which uses 64kb for samples.

The OS by default configures this as 15 stereo channels and uses the remaining two channels as interrupt counters; the IIGS is therefore often described as a 15-channel machine.


Apple Inc.
1998 apple logo.png
Desktop: Apple IApple ][ Line (Apple IIGS) • apple /// LineLisaMacintosh line
Mobile: iOS