Paulo Constantino's Sol-1 Is a True DIY Computer Built from 74-Series TTL Chips and Running a New OS

Vintage computing enthusiast Paulo Constantino has published schematics and source code for a true do-it-yourself computer, built from the ground up to run a custom operating system with parallel processing — using 74-series transistor-transistor level (TTL) logic chips.

"Sol-1 is a homebrew CPU and minicomputer built from 74HC logic," Constantino explains of the project. "The system is built on multibus wire-wrap cards. There is a UNIX-like operating system (still under development), an assembler, and a C compiler (still under development but mostly functional)."

The Sol-1 system — no direct relation to the Sol-20, an Intel 8080-based "terminal computer" developed by Processor Technology and generally recognized as being the first all-in-one personal computer on its release in 1976 — is a maze of wire-wrapped logic chips, eschewing modern microprocessors in favor of doing all its logic in 74-series TTL.

The machine includes two serial ports, two parallel ports, an STMicroelectronics M48T02 Timekeeper real-time clock, a programmable timer, an interface for Integrated Drive Electronics (IDE) hard drives, and a Yamaha AY-based sound board along with its ability to output to an external monitor or controlling terminal. There are eight external interrupts, a single direct memory access (DMA) channel, and support for eight- and 16-bit multiplication and division instructions as well as instructions for fast indexed string handling inspired by those of Intel's x86 architecture.

All of that is enough, impressively, to host an operating system entirely as custom as the hardware on which it runs. The Sol-1's OS, inspired by UNIX, includes both an unprivileged user and privileged kernel mode, support for multitasking with up to 256 parallel processes at any given time, paged virtual memory with a limit of 64kB per process, and both an assembler for machine-code programming and the aforementioned "mostly functional" C compiler.

"I plan to port the original Colossal Cave adventure [to the Sol-1], as well as many other text-adventure games in the near future," Constantino notes, referring to the 1976 interactive fiction originally developed by Will Crowther for Digital's PDP-10 mainframe and considerably expanded in 1977 by Don Woods.

More information on the Sol-1 is available on the project website, while schematics and source code have been published to GitHub under the reciprocal Creative Commons DEED Attribution-NonCommercial-ShareAlike 4.0 International license.

Constantino has also made available a CPU emulator, SystemVerilog source for hardware emulation or implementation on an FPGA, and has connected the original Sol-1 to the internet for public use over the telnet protocol — though at the time of writing the machine was unresponsive.