Engineer and classic computing fanatic Dr. Scott M. Baker has created what might be essentially the most over-specified Heathkit H8 microcomputer in historical past, one way or the other packing 16MB — not kilobytes, however megabytes — of reminiscence within the 70s eight-bit machine.
“I needed to see how a lot RAM I may stuff into an previous eight-bit [Heathkit] H8,” Baker explains. “My unique plan was to construct 4 boards, and have or not it’s 32 megabytes, however because of a small error within the board design, I ended up with solely two boards, for a complete of 16MB.”
Initially launched in 1977 as a build-it-yourself equipment of elements, a inventory Heathkit H8 runs Digital’s CP/M working system on an Intel 8080A processor and required a static RAM (SRAM) card with simply 4kB of reminiscence on board to be able to really obtain a lot. Simply one in every of Baker’s new boards, in contrast, provides 2,048 instances as a lot reminiscence — and he is fitted two of them to his private machine.
The boards themselves are constructed out of a mixture of SRAM and flash reminiscence chips, with roughly equal efficiency — although the SRAM writes extra rapidly and with much less faffing round in software program, however the flash can preserve its contents even when the facility is switched off. Along with the 4 2MB banks, every comprised of 4 512kB SRAM or flash chips, the board contains chip choose turbines, bus and deal with programmable logic units — “I used GAL22V10,” Baker notes, “that are interval applicable to the early Nineteen Eighties,” — and 74-series chips for deal with and knowledge buffers.
“So what is that this good for? Do you really need 16MB of RAM in an H8? In all probability not,” Baker admits. “However you’ll be able to simply use it as a sequence of RAM disks, every one in every of them 2MB in measurement. That provides you room for about eight RAM disks. May you really use 16MB for a function aside from a RAM disk? I’m certain you possibly can… The reminiscence is pageable in 16kB pages, so you possibly can simply swap knowledge or code out and in of reminiscence.”
In idea, as much as 4 boards may very well be put in in a single system for as much as 32MB of RAM. (📷: Dr. Scott M. Baker)
This is not the primary reminiscence enlargement board Baker has designed for the Heathkit H8, although it is by far the biggest. Late final month he showcased the H8 Hellboard, which provided a period-appropriately-generous 64kB of RAM for the system — one-256th of the reminiscence capability provided by Baker’s newest improve.
The identical Heathkit H8 has acquired different upgrades previously, too. Again in March Baker confirmed off a Raspberry Pi-based add-on which allowed for high-speed file switch, whereas in late 2022 he designed and confirmed off a {custom} speech synthesis board for the system.
Full particulars on Baker’s construct can be found on his web site, whereas a schematic, Gerbers, and the PLD supply code can be found on GitHub underneath an unspecified open-source license.
