Prototype new Apple /// memory board

Alexandre Souza alexandre.tabajara at
Wed Aug 25 15:30:40 CDT 2021

Eric, you could have used the 512KB sram chip instead of 4 128KB ones...

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Em qua., 25 de ago. de 2021 às 17:28, Eric Smith via cctalk <
cctalk at> escreveu:

> I've been working on a new memory board for the Apple ///, using (somewhat)
> modern and still-in-production components, especially CMOS static RAM
> rather than DRAM. Last night I soldered the connectors, sockets, and
> passives of my first prototype:
> I need to do some testing for shorts, etc. before I attempt to actually use
> it in an Apple ///. I expect that some debugging of the design will be
> required.
> The Apple /// design is _much_ more complex that the Apple II and IIe. I
> intended this board to provide 512KiB of RAM, but I've already determined
> that some design changes will be required for that, so this prototype will
> only support 256KiB.
> The early Apple /// design, as documented in US patents, would have
> supported up to 512KiB of RAM, but the actual shipped design reduced that
> to 256KiB. There was a third-party 512Kib emory board from "On Three",
> which required pulling various chips from the motherboard and running
> cables from those to the memory board.
> The SOS operating system, as shipped, only supported 256KiB. On Three
> modified the SOS bootloader to detect and use 512KiB. Some Apple ///
> application software also had trouble with 512KiB, and On Three patched
> some of those.

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