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2 MB RAM Expansion for Mac 512K with Dove MacSnap

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Want to get some funny looks from people in the vintage Mac community? Go around telling them you have a Mac 2048Ke! What? Laughing Ok, so that doesn't roll off the tongue so smoothly, but the point is that 512K of RAM is not the limit for a Macintosh 512K! Here at the Mac 512K Blog, we are going to show you how to exceed the limits and upgrade your RAM beyond half a megabyte using the Dove MacSnap.

But first, a

Brief History of Super-512K RAM Upgrades

The Motorola 68000 inside your Macintosh 512K has a 24-bit address range, meaning it can address 16 MB of memory locations. Within the Macintosh memory map, only 4 MB is reserved for RAM; the remaining address space is reserved for ROM and hardware I/O.

In Fatten Your Mac, we talked about the original memory upgrade from 128K to 512K in fall 1984. But the fact remains that 512K of RAM is not the limit, and 1 MB or more is entirely possible. Such a Macintosh, sporting more than 512K of RAM, was known as an Obese Mac, as it was fatter than a Fat Mac!

Apple did not design the Macintosh to be expanded beyond 512K of RAM for the practical reason that there was no room on the motherboard to add more memory, and the board itself was not designed to be expanded or added-on to. Subsequently, the original 64K ROM assumes only 2 possible RAM configurations: 128K and 512K.

Levco Enterprises, Beck-Tech, MicroGraphic Images Corp, MacMemory, Dove, and several other firms all had 1 or even 2 MB upgrade boards for Macintosh in 1985 and 86. These upgrade boards featured 24 or 48 additional 256 kilobit DRAMs and attached to the main Macintosh motherboard. Some of these upgrades required soldering, while others merely clipped over certain ICs on the Macintosh board. George Erhart posted a brief survey of just 4 of these memory upgrades in October 1985.

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Category tags: Hardware, Hacking

Comments

pehrja
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Post 08 Jan 2023 3:37 pm   

Great article! Which of course begs the question "where would one come up with such a device other than by sheer luck of finding one on EBay?" Is there a way, with modern components, to build something that would do the same thing?

Dog Cow
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Post 10 Jan 2023 4:38 pm   

pehrja wrote:
Great article! Which of course begs the question "where would one come up with such a device other than by sheer luck of finding one on EBay?" Is there a way, with modern components, to build something that would do the same thing?

I don't have any exact numbers on availability, but in my experience there is a fair number of these boards still out there, and some are still in Mac 512K or 512Ke units.

The Dove MacSnap board that I show in the article uses all standard ICs, and ought to be cloneable today. Probably you could consolidate the DRAMs too and reduce chip count.




Moof! Moof! Dogcow!

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Post 29 Nov 2023 2:41 am   

Dog Cow wrote:
pehrja wrote:
Great article! Which of course begs the question "where would one come up with such a device other than by sheer luck of finding one on EBay?" Is there a way, with modern components, to build something that would do the same thing?

I don't have any exact numbers on availability, but in my experience there is a fair number of these boards still out there, and some are still in Mac 512K or 512Ke units.

The Dove MacSnap board that I show in the article uses all standard ICs, and ought to be cloneable today. Probably you could consolidate the DRAMs too and reduce chip count.


Yep, I can attest to having one of the Dove Boards in the wild and in perfect working condition. I found this website post in trying to google what the hell it was! Was installed by my father in the 1980's in an original M0001. Recently did some minor restoration work to fix the battery and replace a long-broken internal drive, and the system is usable and reliable.

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Post 05 Jan 2024 2:41 pm   

Can you use a 524 board in a 512KE? Or do you have to have a 524E board for it to work?