The physical constraints of hardware logic

In a TikTok post by @charleszheng0, the author explains how silicon is processed into transistors to perform binary logic. The content describes how billions of these switches form gates, arithmetic logic units, and memory to execute programs at high speeds. It traces the progression from raw material to the functional components of a modern processor.

How it works

Modern computing relies on a linear progression of hardware logic. It starts with the transistor, a switch that uses voltage to represent binary states. By arranging these switches, you create logic gates that process signals into arithmetic. These circuits form an Arithmetic Logic Unit (ALU) for calculation and loops for memory. A control unit coordinates these components by fetching instructions from a program stored in memory. To manage speed differences between storage and processing, a cache sits near the CPU. Input and output devices then translate these binary operations into human-readable data like video or audio.

1. TransistorsThese switches turn on or off to create 1s and 0s.
2. Logic GatesCombinations of transistors perform AND, OR, and NOT operations.
3. Arithmetic Logic UnitCircuits that use logic gates to perform addition, subtraction, multiplication, and division.
4. MemoryLoops of NOT gates that store bits at specific addresses.
5. ProgramA list of instructions stored as binary data in memory.
6. Control UnitA component with a clock that fetches, decodes, and executes instructions.
7. CacheSmall, fast memory located next to the processor to reduce data retrieval time.
8. Input and OutputComponents like cameras and screens that interface the binary system with the physical world.

What it takes to run

A processor does not function in isolation. It requires a physical infrastructure to manage the flow of data between the chip and the outside world. You need a power supply to maintain the voltage levels that define the binary states. You need a motherboard to provide the physical traces that connect the CPU to the cache, memory, and storage. Software engineers must provide the instructions that the control unit fetches. These instructions must be compiled into a machine-readable format of 1s and 0s. Finally, you need a system for maintenance to ensure the hardware remains stable and the software remains executable.

• A stable power source to provide and regulate voltage
• Physical circuitry and traces to connect components
• High-speed storage for long-term data retention
• System memory for active data access
• Input devices to capture external data
• Output devices to render data for users
• A compiled instruction set for the control unit to execute

Where it breaks

Hardware logic operates within physical constraints that software abstractions often hide. As you pack more transistors into a smaller area, heat becomes a primary failure mode. High power density causes thermal throttling, where the control unit must reduce the clock speed to prevent physical damage. Furthermore, transistors are not perfect switches. At microscopic scales, electrons can tunnel through barriers, leading to leakage current. This creates noise that can flip a bit from a 1 to a 0 without a command. You also face the physical limit of signal propagation; electricity cannot move instantly across a motherboard. If the distance between the CPU and memory is too great, the system stalls while waiting for data to arrive.

• Thermal throttling limits the maximum instructions per second.
• Electron leakage causes bit flips and data corruption.
• Signal latency creates bottlenecks between components.
• Voltage fluctuations can destabilise the logic gates.

How we would build it

We approach technical content by mapping the hierarchy of the system. You cannot explain a high-level software output without first defining the hardware constraints that allow it to exist. When we produce content for engineers, we strip away the marketing layer to focus on the data path. We identify the specific components, the protocols they use to communicate, and the physical limitations they encounter. This ensures the information remains useful for someone who actually builds the systems.

1. Map the data flowWe identify every point where data changes state or moves between components.
2. Define the constraintsWe specify the physical or logical limits, such as latency or thermal overhead.
3. Identify the protocolsWe name the specific standards that govern how different parts of the stack interact.
4. Verify the logicWe ensure the sequence of operations follows the actual execution path of the hardware.

Hardware limits will remain fixed for the next year. You will see no change in signal propagation speeds or thermal ceilings. These physical constants stay the same until we find new materials to build with.