The IIgs (or IIGS) is the last of the Apple II line.

The Apple IIGS personal computer is the most powerful, most colorful Apple II ever made. Combining the best of the previous Apple II computers - built-in accessory ports for easy addition of peripherals, and versatile expansion slots for system customization - the Apple IIGS provides an easy-to-use interface similar to that of the Macintosh personal computer. It also offers powerful features such as high-resolution color graphics, 15-voice sound capability, and the advanced 65C816 microprocessor.

The Apple IIGS features GS/OS; an operating system developed exclusively to take advantage of the computer's hardware features. GS/OS offers high-performance capabilities such as rapid disk access and program launching, while increasing the system's ease of use. Powerful hardware capabilities and advanced system software that puts them at your fingertips: It all adds up to the ultimate Apple II personal computer.

Features

Powerful 16-bit 65C816 processor
Compatible with the 65C02 microprocessor used in the earlier Apple II systems
512 kilobytes of user memory (RAM)
Seven general-purpose expansion slots
Seven peripherals ports
One dedicated memory expansion slot
Built-in 32-oscillator sound chip
Built-in speaker and standard output jack for external speakers or headphones
Two super-high-resolution graphics modes, offering a palette of 4,096 colors

General Information

The "Woz Edition" units are part of earlier production and will most commonly contain a ROM 00 board unless otherwise upgraded.

The Apple IIGS personal computer features the Apple IIGS System Software Version 4.0, which includes the following:

GS/OS operating system - Exclusively created for the Apple IIGS personal computer, GS/OS dramatically increases the speed of both disk access and program launching. It also includes File System Translators (FSTs) that allow applications to directly access files created using other file systems, such as the ISO/High Sierra file system used by CD-ROM devices.
Finder - The Apple IIGS Finder has been revised extensively to take full advantage of the GS/OS operating system. In addition to providing support for disk partitions and other new features, the Apple IIGS Finder is now easier to use, faster, and more informative than the earlier version.
Advanced Disk Utility - With its graphics-based interface, the Advanced Disk Utility makes it easy for you to initialize, name, erase, and partition hard disks, as well as to work with both 5.25- and 3.5-inch floppy disks.
Installer - This program allows you to update your startup disks with the latest system software. It also lets you add special system files to customize startup disks for use with your particular system configuration.

CPU

Microprocessor: 65C816
Clock speed: 2.8 or 1.02 megahertz; user-or software-selectable
Address bus: 24 bits
Data bus: 8 bits
Address range: 16,777,216 bytes
16-bit registers: accumulator, two index registers, direct register, stack pointer, and program counter
8-bit registers: data bank, program bank, and status
Addressable memory: up to 8 megabytes of RAM (random-access memory) and up to 1 megabyte of ROM (read-only memory)

Memory

512K of RAM, expandable to 8 megabytes
128K of ROM, expandable to 1 megabyte

Audio

Ensoniq 32-oscillator digital synthesizer chip with dedicated 64K RAM
- Produces up to 15 voices simultaneously
- Uses internal speaker, or external speaker or headphones via audio output jack (volume is set through the Control Panel)

ROM Versions

ROM 00 - Cannot run GS/OS, can be upgraded to ROM 01 via chip replacement.
ROM 01 - Can run GS/OS.
ROM 03 - Can run GS/OS and is the best option for doing so for stability and compatibility.

Expansion

With the video and disk drive ports included on the IIgs board, the system features a number of available expansion slots for use. Modern upgrades include Compact Flash storage, sound cards, etc. Also see these specific options:

TransWarp GS - processor upgrade
Sequential Systems RAM GS - memory upgrade
AST-VisionPlus - video input card
Digital Vision ComputerEyes - video input card

Notes

Hidden IIgs Secrets

When you get the "Check startup device" message after booting your computer, press Control-Open-Apple-Option-N to see the names of the people on the Apple //gs design team
Press Control-^ and then any key and the cursor will change into the key you pressed
While in the monitor, enter a '#', and whenever you access the control panel, you will have two new options, "Memory Peeker" and "Visit Monitor" "Visit Monitor" allows you to do just that, and "Memory Peeker" lets you look at the stack and whatever memory location you desire.

Troubleshooting/Repair

Power supply line filter capacitors risk of exploding

These components on IIgs power supplies are prone to blowing randomly due to age and this will cause a giant mess inside the PSU potentially damaging other components. According to http://damntechnology.blogspot.com/2017/06/replacing-line-filter-capacitors-on.html the replacement part for the paper type is PME271Y510MR30 - Kemet Safety Film Capacitor - Paper - 0.01 uF - 250 VAC - Class Y2 or you can choose the more modern polypropylene F17103101000 - Vishay Safety Film Capacitor - Polypropylene - 0.01 uF - 250 VAC - Class Y2 one.

Vendors such as ReActive Micro also sell universal Apple II PSU kits which replace all the internal components with a newly designed board. See https://www.reactivemicro.com/product/universal-psu-kit/ for details and ordering.

Apple IIgs

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