As a long-term project, I'm designing a barebones "museum piece" computer I call the 2N2/256 BSCP, a bit-serial machine along the lines of an LGP-30, Bendix G-15, or Packard Bell PB-250. To keep costs down and keep it interesting, I want to use only components that would have available to mere mortals in the mid sixties (no ICs except those few commonly available to hobbyists ca. 1965). I'm limiting my madness to discrete transistors, specifically the 2N2222. I'm further limiting the number of transistors semi-arbitrarily to 256.

Don’t laugh! Bit serial machines used an amazingly low number of flip-flops (less than twenty in the case of the LGP-30). Most of the logic was done using diode-resistor AND and OR logic plus an occassional invertor. Flip-flops provided as many of the inverted signals as possible to cut down on transistors. Several of the first transistor computers built had less than a hundred transistors.

The 2N2/256 name is a nod to ham homebrewer Jim Kortge (K8IQY) who designed a QRP rig called the 2N2/40 for a design contest about ten years ago. The contest objective was to design and build a functional amateur radio transceiver, using a maximum of 22, 2N2222 type transistors. My long-term challenge is to build a complete functional computer, including memory, using no more than 256 2N2222-ish transistors. Of course there will be a pile of si diodes, resistors and capacitors involved, but the idea is to keep the number of active components down -- if only so this beast will fit in the boot of my car! Toward that end, I am building everything to fit in 350mm cube modules.

I've scavenged the web for information on bit-serial magnetic drum/disk machines of the Elder Years, and I think I have a pretty good notion of how they worked (mostly very slowly). What I haven't been able to get a handle on (yet) is how to make a serviceable magnetic drum/disk. To get things going I reckon I’ll emulate the drum with some CMOS shift registers so I don't have to debug both the logic and the magnetic read/write electronics at the same time.

That leaves the CPU. So, this month my goal is to build enough flip-flops and logic to implement a basic 16-bit ALU with 2's complement arithmetic and logical functions. This in itself wouldn’t be much more than a weekend project but for the fact that everything has to be done bit-serially!