This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
The IIgs (or "GS") represents a giant leap in the Apple II line. It's 65C816 microprocessor can switch to 6502-emulation mode for running 8-bit Apple II software favorites, while, in native mode, it runs 16-bit GS applications. GS delivers new super-hires graphics modes, a toolbox in ROM, a 32-oscillator Ensoniq sound chip, and a max base speed of 2.8MHz. Base RAM memory is 256kB (ROM-01) or 1MB (ROM 3) expandable up to 8MB. GS built-ins include modem and printer serial ports good for up to 230k baud, Disk Port supporting two 5.25" and two 3.5" (800k) drives, RGB and composite video outputs, enhanced and 'old Apple' sound, ADB bus for keyboard and mouse, game port supporting two two-button joysticks, clock/calendar, and battery RAM to retain user settings accessible via the Control Panel. (To get to the Control Panel press OpenApple-Control-Escape and select "Control Panel".) There is more about Apple IIgs specifications in the FAQs resource file R024GSSPECS.txt. The IIgs can run DOS 3.3, ProDOS, Pascal, and any other OS the earlier 8- bit models can run. In 8-bit or "emulation" mode, it works much like an enhanced //e, even down to supporting nearly all of the old monitor routines and softswitches. One notable difference is that users must go to 64k Bank $FF (e.g. FF/F800 - FF/FFFF) to view monitor ROM contents. In the default (Bank $00) area, an F800L etc. monitor command shows code in the "Language Card" RAM. Like the //c series, it does not support the ori ginal Apple casette tape I/O. GS is the only A2 machine which can run GS/OS. GS/OS and Toolbox routines make it possible for the System Finder program to deliver a sophisticated 'mouse and windows' environment which looks very much like PC's Windows. The current version of System is System 6.0.1. The first GS's were released in the Fall of 1986. The batches produced until mid-late 1987 became known as "ROM 00" machines after release of the "ROM 01" models. When you turn ON or force restart a ROM-01 GS, the startup screen shows "ROM Version 01"; on a ROM-00 GS the startup screen says nothing about ROM version. (Press OpenApple-Control-Reset to do a forced restart.) The original GS's came in cases marked "Limited Edition" with Steve Wozniak's signature. Often, these are referred to as "Woz GS's". (See FAQs resource file R002WOZGS.GIF for a picture.) Only about 50,000 ROM-00 IIgs's had the "Woz" signature. A relatively small number of users chose Apple's option to upgrade their //e's with a motherboard swap. Introduced in early 1987, the upgrade included "IIgs" labels which users could substitute for "//e" in the case insert. At the time of the ROM-01 change-over in 1987, Apple supplied a ROM-00- to-ROM-01 upgrade service free. It consists of swapping in a new ROM and a new Video Graphics Controller ("VGC") IC. ROM-00 machines which have not had the upgrade can not run modern GS software-- the ROM must be upgraded. Alltech (760-724-2404; http://allelec.com ) is a good place to check for a ROM-01 'upgrade kit' consisting of the 01 ROM. (Price: around $30.00) The VGC upgrade is not required for software compatibility, and is not needed for all machines anyway. It is supposed to fix cosmetic problems in monochrome double-hires graphics mode (pink flickering or fringing on what is supposed to be a black and white screen). On some machines the VGC swap also fixes some color combination problems in 80-column text mode. Note: ROM-00 machines can boot disks which start System up through Version 3. (Booting these disks typically starts by displaying some version of "ProDOS 16".) The downside, of course, is being unable to boot modern versions of System and use software which needs to run under the later versions. On the other hand, a number of very early products run under versions of System which have no patches for ROM-01 or ROM 3. Original diskettes for these products will boot correctly only on a ROM-00 GS. Whether via the upgrade or original purchase of a newer GS, by late 1987 nearly all GS users were 'on the same page'. That is, we had the ROM-01 platform with its base 256kB RAM plus the official Apple 1MB Expansion Memory Board plugged into the Memory Expansion Slot for a total of 1.25MB of fully- accessible system RAM. For the next couple of years, practically all GS software was designed to launch from 3.5" diskette under "ProDOS-16" and to fit within the 1.25MB of RAM everyone was assumed to have installed. In 1989 Apple introduced the "ROM 3" GS-- the startup screen shows "ROM Version 3". (No ROM-02 GS was ever released). The only major improvement over ROM-01 is more base RAM-- you get 1MB instead of 256kB. This is a very nice benefit. It means that a ROM 3 with a 4MB Mem Exp Board will have 5MB of fully accessible RAM whereas a ROM-01 can have 4.25MB of fully-accessible RAM. In effect, the ROM 3 owner gets a 'free' 800kB RAM disk. As Mitch Spector notes in his listing of ROM 3 features (in the "Hardware Hacking" FAQs), the newer GS offers a number of other nice pluses with the only significant minus being incompatibility with a few older GS programs and pre- System 5 versions of GS System. Chiefly, ROM 3 is a 1989 re- do of ROM-01 featuring more streamlined hardware and more built-in firmware. Since System 5, booting GS System applies in-RAM patches matched to ROM version 1 or 3. The patches, located in System/System.Setup/, are TS2 for ROM- 01 and TS3 for ROM 3. This achieves nearly identical operation. Very few ROM-01 owners felt any urge to move to ROM 3. Even today, the vast majority of installed GS's are ROM-01 machines. The 1990's saw wide adoption of four major GS enhancements: OS- After years of foot-dragging, Apple finally produced a decent 16-bit GS operating system with release of System 5.0. Within a few years this evolved into today's System 6 (System 6.0.1). System 6 has won wide acceptance as a relatively stable OS which, at last, allows GS users to access many of the features of GS computing promised back in 1986. Although any ROM-01 or ROM 3 IIgs with at least the 1MB Apple Expansion Memory card installed can boot a fairly decent install of System 6 from diskette, the f act that it is likely to use at least 800kB of RAM somewhat limits the applications which can be run, especially on the ROM-01 GS. Memory- Driven, in part, by the need for more memory to run System 6, 4MB became the standard size of installed Memory Expansions. Except for school GS's and GS's taken out of circulation and tucked away in closets, the old Apple 1MB Expansion Boards have long ago been replaced with boards adding 4MB- 8MB. Hard Disk- As with memory, the size of newer versions of System supplied a strong push toward adding a hard disk. Software was becoming larger, too, and there was so much of it that making everything work from diskette became impossibly cumbersome. Lower HD prices, attractive SCSI interfaces such as RamFAST, and low-cost, easy single-card IDE solutions such as the Focus "Hard Card" and SHH Systeme "Turbo" cards have helped make the hard disk a standard, expected peripheral on today's GS. Acceleration- Few commercial software offerings actually sought to push GS users to higher speeds; and, as a result, users went for years feeling no great need for Applied Engineering's expensive Transwarp accelerator. The arrival of Zip Technology's lower-cost ZipGS board together with a clear need for more speed to handle System 6 sparked a nearly overnight 'acceleration revolution'. Today, an accelerator running at 8MHz or better is considered, very nearly, to be a necessary IIgs enhancement. Recommended configuration: ROM-01 or ROM 3 with 4MB or 8MB Memory Expansion board-- i.e. at least 4.25MB (ROM-01) or 5MB (ROM 3) of total system RAM, RamFAST SCSI + 120MB or larger SCSI hard disk OR 120MB or larger HD-on-a-card IDE drive (e.g. Alltech's Focus Hard Card or SHH's Turbo IDE series) with System 6.0.1 installed, 8MHz/32k TransWarp or 9MHz/32k ZipGS or better accelerator board, Stereo Card, Imagewriter II printer, two 3.5" and two 5.25" diskette drives. A minimum GS system that will run many older wares and still deliver a decent operating system is a ROM-01 GS with the Apple 1MB Memory Expansion board, two 3.5" drives, at least one 5.25" drive, and Imagewriter II printer, which boots System 5.0.4 or System 6.0.1 from 3.5" diskette. --Dan DeMaggio, Rubywand, David Empson, Supertimer, Randy Shackelford, Hal Bouma Related FAQs Resources: R028LCA2CARD.TXT (text file)