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Old Dec 18, 2012, 02:41 PM   #1
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Rom 3 IIGS - 256KB or 1MB on motherboard?

When Apple released the Rom 3 version of the IIGS it came with 1MB of ram?

Not clear if that was a new motherboard design with 1MB on it
or a standard 256KB motherboard with a 1MB card?
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Old Dec 18, 2012, 04:58 PM   #2
David Schmidt
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Originally Posted by OSMac View Post
When Apple released the Rom 3 version of the IIGS it came with 1MB of ram?
-ish. A little more than 1MB is built in.
Originally Posted by OSMac View Post
Not clear if that was a new motherboard design with 1MB on it
or a standard 256KB motherboard with a 1MB card?
It was a new motherboard design. ROM00 and ROM01 are the same mobo, but ROM03 was a new one.
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Old Dec 20, 2012, 12:03 PM   #3
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The ROM 3 is a slightly redesigned board:

Newer ADB Micro Controller that could support newer ADB devices and provided more performance options.
Repeat speed/interval
Reverse CapsLock with the shift key.
Key Repeating, delay and speed
Cursor tracking speed - more settings than the previous.
Numeric Keypad mouse control

Firmware revisions, though still not "current" at shipping time as the System Software release had revisions of many of the inbuilt toolsets.
Twice as much onboard firmware as the previous revision

The 65816 can address 16MB total RAM, and the IIgs was setup so that the first 8MB could be RAM space and the second 8MB was ROM space, that could be expanded via hardware just as the RAM, from the same slot. The typical idea was a static storage volume in ROM, hence 'ROM Disk'. The other ability was to add/supplant the onboard toolsets. During the boot process, if the Toolset about to be loaded is present in ROM, and is the same or newer, the disk version is skipped. If all of the current toolsets are in ROM, then the computer can boot faster. When working with a floppy disk this could be huge if most/all the Toolsets were onboard.

The "ROM 01" system is built around System Disk 1.0, and the ROM 3 is built around System Software 5.0.

The "ROM 01" has 256K RAM and the ROM 3 has 1.128M RAM.

The "ROM 01" has 128K of "Slow" RAM, and 128K of "Fast" RAM. The Fast RAM was upgraded to 1024K, bringing the total to 1.128M. Since the "slow" side needed to retain the original specs for the intended compatibility, that resulted in the odd-seeming amount of RAM.

Of course this also ate into the 8MB of RAM space, so if an 8M capacity card is added you still only have 8MB usable. Not the 9 that may be physically present. This also invoked a firmware bug where the RAM disk would not be established if it were enabled with the computer having more than 7168K installed.

On many emulators, the maximum RAM can be changed to 14MB with the final 2048K being reserved for the ROM space. The firmware change for this is just 1 byte, and since it's all virtual, it can work. Of course, the emulator application itself has been re-worked for it.

Where as with hardware, the addressing capability is not present on the motherboard, both via the slot and other onboard designs. It's relatively straight forward to change, but hardware is generally static. Wire wrap and board modifications would need to be made, and the firmware patched.

The slot configuration got a little more dynamic with the ROM 3:

Slot 1 and 2 could be selected to each be Printer, Modem, Appletalk or Your Card. Other changes for AppleTalk, mentioned below.
Slot 3 remains the same.
Slot 4 remains the same except the mouse support level was reversed. Instead of the total mouse support "by the book" requiring the slot to be declared "Mouse Port", on the ROM 3 this was reversed to be that declaring it as "Mouse Port" means that 8 bit "Apple Mouse //" compatibility would be extended to software such as AppleWorks, MousePaint, etc. Anything that was expecting a mouse card in Slot 4.

Software such as the FTA demonstrations that were "toolbox free" may also not function fully on the ROM 3 due to the ADB changes, and Mouse control.

Slot 5 remains the same.
Slot 6 remains the same.
Slot 7 remains the same, mostly. On the "ROM 01", when AppleTalk was chosen, Slot 1 needed to be made to be "Your Card" when an AppleTalk choice was made on Slot 7, taking out two slots.

With the ROM 3 you can do this for compatibility with a "ROM 01" AppleTalk solution, though .. I can't even remotely think of anything that would need it. Or you can just choose AppleTalk in Slot 1 or 2 and be done with it.
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