From the comp.sys.apple2 - Frequently Asked Questions (and answers) part 2 of 2 by Dan DeMaggio:
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Code:
The GS represents a giant leap in the Apple // line. It can still run //e
software, but has a better processor (16-bit), a new super-hires graphics
mode, a toolbox in ROM (just like the Mac) and a 32 oscillator Ensoniq sound
chip. It can not only run ProDos, but it can also run GS/OS, a sophisticated
operating system very much like the Macintosh's OS. The original GS ROM 00 (I
think they all have the Woz signature) one or two chips upgraded to boot/run
current software. The ROM 01 had 256K on the motherboard, while the ROM 03
has 1 MB. Although there were a few ROM changes, the current system software
will work patch the toolbox ROMs to look identical.
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Apple //GS:
There are 3 major versions of the GS: Check the initial power-up screen. It
will say ROM 01, ROM 03. If it does not say either, you have the Original
(Woz Signature edition). You must upgrade it in order to run current system
software. The ROM 01 has 256K on the motherboard, while the ROM 03 has 1 MB
on the motherboard. All the enhancements of the ROM 03 (except the 1MB, of
course) can be added to the ROM 01 simply by booting up with current system
software.