The GS represents a giant leap in the Apple II line. It can still run //e software, but has a better processor (16-bit 2.5Mhz 65816; can be slowed to 1Mhz for compatibility with older Apple II programs, especially games), more ram (256K built in to the first releases), a new super-hires graphics mode (320x200, 16 colors per line colors picked from 4096 colors, or 640x200, 16 dithered (4 true) colors per line from 4096 colors), a large set of commonly used routines called the toolbox in ROM (just like the Mac, though it is not identical) and a 32 oscillator Ensoniq sound chip.

Despite having 7 main slots like a //e, plus a RAM card (different from the //e's AUX slot), the GS has 2 serial ports, Appletalk support, a 3.5" and 5.25" disk port, and RGB monitor connector built in, but using those ports required that one of the 7 main slots in it be mostly given up. (Accelerators and video boards didn't require that.) The IIGS can not only run ProDOS, but it can also run GS/OS, a sophisticated operating system with the better features from the Macintosh OS.

With the new processor, video modes, and the like, IIGS software tends to run only on the IIGS and no previous Apple II models, but pretty much all software that runs on a //e or //c will run on a GS.

Released in September 1986, the original GS ROM 00 (which tended to have the Woz signature on the front case, though that is no guarantee) must have one or two chips (the ROM and possibly also the Video graphics controller) upgraded to become a ROM 01 machine and boot/run current software. The first 50,000 GSs sold had a 'Woz' signature painted on the front of the case; this was known as the 'limited' edition. With so many of these cases, there's almost no added value to the limited edition.

A later revision of the motherboard, known as the ROM 3 had a number of significant changes: more ROM (256K vs. 128K) on the motherboard, more (1MB vs. 256K) RAM on the motherboard, different capabilities for the internal slots, better support for the disabled, and a cleaner motherboard which can result in quieter sound support. The extra ROM allows more parts of the system software to be accessed from there, which allows a ROM 3 to boot and run GS/OS and GS/OS programs slightly faster than a ROM 01. (The two have identical toolbox functionality from the programmer's standpoint, however.)

To determine which ROM version you're using, when you power it up, it should say "Apple IIGS" at the top of the text screen for a second or so, and possibly some text at the bottom, which states either ROM 01 or ROM 3. If it does not say either, you have a ROM 00, the original version. You must upgrade a ROM 00 to an 01 (easy-- swap 2 chips), or a ROM 3 (much harder-- a motherboard swap is required, and you might as well purchase a ROM 3 system outright) it in order to run current system software.

There is no such thing as a ROM 02 or 2. The engineers at Apple called the first revision of the GS's ROM a ROM 00, and the second 01. However, many people were confused by the second revision having a 1 in the name. To get things back in sync, the third revision also has the numeral 3 in the name. The ROM 4 existed in several prototypes, but was killed off before general production.

The current system software works to make a ROM 01 and a ROM 3 two systems appear almost identical to the software, except for the obvious such as the amount of RAM built in. Certain games and other copy protected software that used undocumented entry points on the ROM 01 will not work on the ROM 3.

Due to software compatibility reasons, the slots and built in ports are mostly exclusive, unless the board only uses the slot for power but not communicating with the computer (usually only accelerators, some sound boards, and video boards). Slots 1 and 2 are the modem and printer ports, 3 is the 80-column video, 4 is the ADB mouse, 5 is the 3.5" drive support, 6 the 5.25" drive support, and 7 is sometimes used for Appletalk. [ROM 01 requires slot 7 be set to Appletalk, and one of slots 1/2 to 'Your Card', but the ROM 3 can have 1,2 or 7 be Appletalk.] The control panel (accessible by control-open apple-escape) lets you make the decisions as to what mode each slot is in: built-in port or whatever is in the physical slot.

Recommended configuration: 1.25 MB RAM lets you boot up GS/OS and use most smaller programs, though it may be tight. With 2 MB, you will have room for Desk Accessories. Go for 4MB if you want a RAM disk (useful if you don't have a hard drive) or do a lot of graphics work. Adding a hard drive is highly recommended for speed and System 6, otherwise you'll be doing a lot of disk swapping. You can also speed it up with a TransWarp GS or Zip GS, which can speed a GS up to around 14Mhz.

Information Courtesy of the Apple FAQ, Part II