From: Bruce Johnson <[EMAIL PROTECTED]> Subject: Re: [PCI] 7300/180 ROM SIMM Mystery Date: Mon, 14 Jun 2004 08:28:45 -0700
That slot was never used, afaict. Apple *did* intend it to be used for ROM upgrades or replacements, but like many technologies Apple implemented in the 90's it went nowhere and was never used, replaced by the new hardware design du jour, in this case, the G3 Powermacs, which *did* have the ROM on a replaceable DIMM, but a different design one, iirc.
Actually, the G3 ROM slot is nearly identical. The primary difference is that a bunch of unused pins in the x500, x300, x600 slot are allocated to 3.3V in the Beige G3 slot and the G3 uses a 3.3V powered ROM. However, the 5V pins are still available in the G3 slot, they simply aren't used by any of the Apple ROM DIMMs. There's also something funny with pin 122 or maybe 112 and whether the G3 will address more than 512 MB of RAM.
Incidentally, the ROM DIMM is also the same on the x100 series, that is the NuBus PowerMacs. Of course, the ROM code is very different amongst these three families of machines, but the ROM module hardware is nearly identical with the same data, address and control pinouts.
Oh, and the Apple Network Server uses the same ROM module hardware as well, which isn't surprising since it is based on PM9500 hardware.
Jeff Walther
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