Intel 4004 — World's First Microprocessor
A working 4-bit microprocessor in the spirit of the 1971 Intel 4004 — the world's first single-chip CPU. A real stored program (4 × 3 by repeated addition) flows through FETCH → DECODE → EXECUTE → STORE on three tri-state buses, and a dedicated product display steps a clean 0 → 4 → 8 → 12 before the machine halts.
学べること
- Trace a complete fetch–decode–execute–store instruction cycle
- See how a Program Counter, Instruction Register, ALU, accumulator and flags form a CPU datapath
- Understand why a stored-program machine needs disjoint tri-state buses to avoid contention
- Follow how a conditional-jump (zero flag) builds a loop in machine code
- Appreciate the 4-bit architecture that started the microprocessor era
仕組み
This is a complete, if minimal, stored-program computer assembled from DigiSim CPU blocks. A Control Unit sequences every instruction through four states — FETCH, DECODE, EXECUTE, STORE. The 8-bit Program Counter addresses the program held in RAM; each byte is latched into the Instruction Register, whose opcode nibble drives the Control Unit and whose operand nibble addresses data. The genuinely 4-bit datapath — a 4-bit ALU and a 4-bit accumulator with a flags register — does the arithmetic, moving nibbles over three disjoint tri-state buses (address, operand, result) so no two drivers ever fight. The demo program multiplies 4 × 3 by repeated addition and loops using the zero flag. Because the single accumulator is time-shared between the running product and the loop counter, a dedicated product register latches the accumulator only when the product is written back to RAM — so the PRODUCT hex display shows a clean 0 → 4 → 8 → 12 instead of the accumulator’s churn.
実世界での応用
The Intel 4004 (1971) was the first commercially available microprocessor, designed for the Busicom 141-PF printing calculator. Putting a whole CPU on one chip launched the microprocessor era; its core ideas — a stored program, a fetch-decode-execute cycle, an accumulator and flags, and separate program and data memory — are still the blueprint inside every CPU, microcontroller, and phone today.