From Turing to LLMs and Beyond -- Illustration Companion

Von Neumann Architecture

The blueprint inside every computer -- from your phone to a supercomputer

Illustration companion to Issue 2: Building the First Brains

Main Architecture Diagram
SYSTEM CLOCK 3.5 GHz 3.5 billion ticks/sec CENTRAL PROCESSING UNIT (CPU) Control Unit (CU) PC: 0x0042 "Where am I?" 1 IR: ADD R0,R1 "What am I doing?" DECODER "What does this mean?" ctrl signals ALU 2 + - x / AND OR NOT Input A Input B Result FLAGS: Z=0 C=0 V=0 Registers 5 R0 42 R1 17 R2 0 R3 0 R4 0 R5 0 R6 0 R7 0 Fastest memory -- inside the CPU itself 4 DATA bidirectional 64b ADDR 32b CTRL R/W System Bus MEMORY (RAM) 3 ADDR CONTENT 0x0000 LOAD R0, 42 0x0001 LOAD R1, 17 0x0002 ADD R0, R1 0x0003 STORE R0, 0x0010 0x0004 HALT INSTRUCTIONS - - - - - - - - 0x0010 59 (result) 0x0011 255 0x0012 0 . . . 0xFFFF 0 DATA Programs AND data live in the SAME memory! INPUT / OUTPUT I/O Controller Keyboard Display Storage Network Fetch-Decode-Execute Cycle FETCH PC -> Addr Bus -> Memory -> IR DECODE IR -> Decoder -> Ctrl Signals EXECUTE ALU computes Result -> Reg PC increments, repeat forever... 1 2 3 Memory Hierarchy Registers L1 Cache L2 Cache RAM Storage / SSD ~1ns ~2ns ~7ns ~100ns ~50,000ns Faster Bigger Speed vs. Capacity: you can't have both!
1
The Program Counter always points to the NEXT instruction. After each fetch, it increments automatically -- unless a jump instruction redirects it.
2
The ALU can only do simple math -- add, subtract, compare, shift bits. But it does it billions of times per second. Every video game, every AI model, every web page is just the ALU doing simple operations very fast.
3
Von Neumann's big insight: store the PROGRAM in memory, just like data. Before this, programs were hardwired. The stored-program concept means you can change what a computer does just by loading different instructions into the same memory.
4
The bus is the highway -- all data travels on these shared wires. The data bus carries values, the address bus says WHERE, and the control bus says whether to READ or WRITE. Everything shares these three highways.
5
Registers are tiny but blazing fast -- the CPU's scratch paper. There are only a handful (8 here, 16 in x86-64), but they are accessed in a single clock cycle. Everything the CPU is actively working on sits here.