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What is stored in the IIgs BRAM? I'm going to replace my BRAM battery in a ROM 03 IIgs and that got me thinking about what is stored in BRAM. I know that date and time are stored, but not if all the same values are stored on the IIgs as on the Macintosh.

2 Answers 2

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What is stored in the IIgs PRAM?

Basicly everything you can set via the Control Panel

I'm going to replace my PRAM battery in a ROM 03 IIgs and that got me thinking about what is stored in PRAM. I know that date and time are stored, but not if all the same values are stored on the IIgs as on the Macintosh.

It's much like the Mac. In addition to things like language, colours or interface parameters, more hardware related setup values are also stored. This includes speed and asignment of function to slots and so on. For example I remember offset $28 beeing the boot slot.

The only description of the data I could find is the description of the control panel in Apendix G of the IIgs Firmware Reference (p299ff). But it goes only by the handling of said ROM programm, not how it's stored. You might want to do some web search to find more. When doing so it might be a good idea to include BRAM as term, as it was thuout documentation usually called 'Battery RAM' (*1).

AFAIR the first $20 are the clock part and the control panel uses the area up to $60 or so. Everything thereafter is initialized with $FF. Except for the last 4 bytes containing some checksum.

A helpful tool might be Sheppy's Shifty-List, as it, IIRC, allows it to save and restore BRAM content among many other setings, so you won't have to worry to miss anything.


*1 - BRAM vs. PRAM is a nice little way to distinguish old time Apple IIgs fellows from Mac people.

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The official list of BRAM values can be found in the Toolbox Reference Volume 1 in Table 14-3.

This list was extended in System 6.0 and 6.0.1, which is documented in the Programmer's Reference for System 6.0.x.

A combined list can be found in Neil Parker's document on the subject.

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  • 1
    your second link doesn't go to the reference you mentioned
    – scruss
    Dec 6, 2023 at 14:50
  • Apple started with documentation in APDA (Apple Programmers and Developers Association) and Addison-Wesley. Later on they outsourced the documentation to the biggest Apple IIGS development tools company at the time called "The Byteworks" (en.wikipedia.org/wiki/The_Byte_Works). The Opus II collection contains all of the software that The Byteworks produced plus all of the documentation they produced. The documentation includes the official (outsourced) Apple documentation.
    – Ian Brumby
    Dec 7, 2023 at 21:27
  • it's not a reference if I have to pay to download it. This looks like a link, but the table only has two items in it (p.49): apple2.gs/downloads/library/…
    – scruss
    Dec 8, 2023 at 1:26

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