8-bit

An 8-bit computer designed and built from scratch on breadboards, featuring 1MB of RAM and a VGA-compatible video board.

About

This is an 8-bit computer built on breadboards from 7400-series logic chips. It has 20-bit memory addressing and 8-bit-wide data paths.

Stats:

20 breadboards
Around 70 ICs, all 74HCxx series except for 2x AS6C4008 512Kx8 SRAM, 2x SST39SF040 512Kx8 flash, and one 74AHCxx chip
Numerous LEDs displaying the internal state of the CPU (although some of these were removed later on in development).
~250 feet of 22 AWG solid-core wire, plus some jumpers
Total materials cost of around $150

Capabilities:

Non-pipelined operation with two clock cycles (fetch and execute) per instruction
512K x 16 bits flash memory, 512K x 16 bits RAM
Multiple addressing modes
Six ALU operations: add with carry, and, or, xor, rotate right, and compare
1.5 MHz stable clock speed
Flexible expansion boards, configured with a VGA board, PS/2 keyboard input, and an extra timer

Stats:

9 breadboards
A lot of ICs, mostly 74Fxx series with some 74HCxx series and one AS6C1008 128Kx8 SRAM
Nearly 150 feet of 22 AWG solid-core wire
Exactly one LED

Capabilities:

640x480 color VGA output via a standard VGA connector
80x60 grid of characters (128x128 in memory)
Up to 256 characters, 8x8 pixels each
16 colors (RGBI); two can be selected (foreground and background) per character cell
Pixel-level scroll registers for both X and Y

See v3/ for full schematics of and the PCB design for the main CPU. The VGA board is documented separately here.

See software/. Most notably includes a Z-Machine for playing a wide variety of text adventure games.