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Macintosh Classic Onboard RAM upgrade?! Eh?

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The address map for the Classic puts ROM at the 4mb mark, so it's kinda stuck to 4mb. All the 68000 macs use this address arrangement, with the exception of the Portable. The Portable is the odd one here, where it maps ROM at the 9mb mark.


In the 68000 machines you can't really rearrange addresses since there's no MMU. You can't remap the hardware registers, so things are kind of stuck.

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. . . or the PowerBook 100's 8MB?


Interesting that they bumped the Lit Up Luggable to 9MB, if that was due to higher density memory in that same SRAM package. This seems to be the case with the MoBo DRAM upgrades that work.


As I understand it, uni's soldering four on the floor and soldering anther four on the door which already has slots for another two 1MB SIMMs. That would be a 10MB maximum loadout by my count.


The Classic shipped the same day as the LC, which does 10MB on a 68020 w/o a PMMU . . . hrmmm . . .

. . . I wonder if there is any chance that the two share that same broke-@$$ Memory Controller kluge? :?:

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Just because the Classic, LC, and IIsi were released together doesn't mean they share any architectural similarities.

The IIsi uses the MDU memory controller found in the Iici.

The Classic uses the BBU memory controller (well, calling it a memory controller is a stretch, it acks some bus accesses and moves physical ram around so the machine can boot out of ROM) found in the SE.

The LC was the first with the new memory controller also used in the LCII.


The physical locations of hardware are also their logical locations in machines without an MMU. Hardware lives at physical addresses, those don't change. An MMU, the processor can present a logical view that differs from the Physical view. Without an MMU, the two are necessarily the same. The memory controller in all macs going back to the 128k do some amount of moving the address space around, for example although ROM physically lives at 0x400000, the memory controller makes it available at 0x0 on boot so the processor can boot from it, then moves the bottom of RAM to address 0x0. The II and the LC memory controllers do a little bit more to allow the 24bit/32bit views of the world.

The Classic has SCSI at 0x580000, SCC registers at 0x900000, IWM and VIA above that. They don't live at the same locations as on a Portable.

The LC, supporting 32bit accesses, has things arranged more along the lines of the Mac II and subsequent 32bit capable machines. The hardware lives in the 0xF00000 range in 24bit mode.

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ok so here is what i have :)


- desoldered the 1meg onboard - 8 chips

- soldered the 4megs of ram, - 8 chips

[attachment=0]Screen Shot 2013-12-31 at 9.40.24 AM.png[/attachment]


- Poped the board back in the classic w/o RAM card installed

! AND she boots!


[attachment=1]Screen Shot 2013-12-31 at 9.27.33 AM.png[/attachment]




However only 2 megs of ram show up.

out of the 4.


So ok, i pop the 3 meg ram card back in…


Flip the classic on…


And she boots!


now it says there is 4 megs of ram installed.



( must be ignoring the one meg soldered on the ram card )


so for giggles i remove the 2 one meg simms.

and change the jumper to simms not installed.

to force it to use the one meg onboard.


and no dice it will not boot.


so here is what i am thinking.


The VLSI POS gives me 2 banks… A and B… but will only allow a maximum of 2 megs per bank.


lol so what do i do… leave the 4megs on there… and just pull the ram card… and sell the ram card to someone in need and maybe just

stick with 2 megs of ram… or… solder the one meg back on and just stick with the ram card, and 4 megs of ram.


well considering the macintosh classic is slow as molasses on a cold winter day… i might just keep that 4 in there…

for a total of 2 meg's and free up this 3mb ram card for a sale…


not ideal but should work… never know what you are going to get with these sob's until you start swapping chips…

next, soon will be classic II experimentation. hoping to bump up the onboard ram to 8megs… i wonder what mysteries that memory controller will show me.

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Yah! The SE was a top flight Compact Mac when it was introduced alongside the Macintosh II. Apple couldn't possibly have let any of that expansion slot goodness or, heaven forbid, even let Killy Klip compatibility sneak its nefarious way into a brand new new design for a Low End Mac priced under $1,000 for heavens sake!

Upgradeable RAM . . . oh my goodness! What were we thinking? :lol:

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