The JDH-8 is a complete hand-built computer assembled from basic logic chips, jumper wires, and 20 breadboards. Its reported design pairs 8-bit registers with a 16-bit address bus, memory, 256 I/O ports, and a simple graphics processor. The project shows how a computer can be organized from logic-gate-level modules—and how much debugging can remain after those modules are connected.
What the JDH-8 is
JDH-8 is a computer project built by a YouTuber known as jdh. Hackster.io describes it as a breadboard machine made from basic chips and many jumper wires, intended to explore how computation can be built from logic gates. The project occupied 20 breadboards when complete. These are reported project details, not independently benchmarked specifications. Hackster.io’s project report is the available account of the build.
How its reported architecture fits together
The JDH-8 combines 8-bit data-oriented registers with a 16-bit address bus. That distinction matters: the register width describes the size of values handled in the CPU’s registers, while the wider address bus is used to identify memory locations. Hackster reports eight CPU registers; as many as seven can serve general purposes, while the remaining register holds status flags produced by the arithmetic logic unit (ALU). Hackster.io’s specifications and architecture summary does not give a clock rate or a measured performance result.
Memory and the stack
The reported memory arrangement includes 16 KB of ROM for programs and 16 KB of general-purpose RAM, alongside stack space. Three words are reserved for the stack pointer, program counter, and current memory bank. The CPU includes a hardware stack with push and pop instructions. The source does not state the complete memory map, so these figures should not be taken as a full reproduction guide. Hackster.io’s architecture account
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Instructions, I/O, and graphics
The CPU uses a load-store architecture: a value must first be loaded from memory into a register before an operation can use it. The report also describes a range of ALU operations and 256 I/O ports, through which the machine can interact with other devices. Its video generator is described as a simple 208×240-pixel graphics processor. No supported instruction count or measured graphics frame rate is stated. Hackster.io’s project report
How the creator planned and built it
The design was planned and emulated before being wired as hardware. The project report describes moving from a schematic divided into functional modules, to representations using gates, latch banks, multiplexers, and other functional symbols, and then to chips and wiring. The modules included:
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- ALU and register file
- Address module and I/O
- Instruction counter and control signals
- Video generator
Each module was laid out on breadboards so it could be tested individually before the larger system was assembled. The account does not identify exact chip models, logic families, or a complete bill of materials; the broad categories it supports are basic logic ICs, solderless breadboards, and jumper wires. Hackster.io’s build description
What happened during testing
When the modules were connected and powered, most instructions reportedly worked, but the graphics output did not. The builder spent eight hours troubleshooting the video and made 20 additional attempts, with several fixes along the way. The eventual test display showed “HI” and a small smiling face. Hackster’s account also says the machine could show images, perform math, and communicate with other devices through its I/O bus. These are reported demonstrations, not a published benchmark of speed, reliability, or image capability. Hackster.io’s build and testing account
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What the builder would change
In the project postmortem, the builder reportedly considered the hardware stack unnecessary, the ALU over-engineered, and the load-store architecture unwieldy. Those are lessons about this design’s complexity and trade-offs, not evidence that stacks, elaborate ALUs, or load-store CPUs are generally poor choices. The report does not provide enough implementation detail to determine how those design decisions affected performance or component count. Hackster.io’s account of the builder’s postmortem
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the project does—and does not—establish
The JDH-8 is a useful example of a computer assembled from logic ICs and breadboarded modules, with CPU, memory, I/O, and video functions brought together in one project. The reported specifications and testing narrative come from Hackster.io’s secondary account; the linked creator videos and design files were not independently reviewed for this overview. Exact parts, source-code details, clock speed, power use, instruction count, and graphics frame rate are not established by that account. Readers seeking to reproduce the machine would need to consult the creator’s primary design materials rather than infer a parts list from the reported specifications.
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