The Intel 4004 at 50
By Kevin Krewell 11.15.2021
November 15th is the 50th anniversary of the launch of the first commercially available microprocessor — the Intel 4004. Our industry can trace itself back to this seminal event, and it’s amazing the progress the industry has made in 50 years. Intel has created a site dedicated to the anniversary that will have links to videos by the early designers and a wealth of information on the development of the chip.
You should be familiar with the story of how Intel engineers Marcian “Ted” Hoff, Stan Mazor, and Federico Faggin, pitched a new design for the Busicom calculator that reduced the chip count from 12 to only four. The CPU had only 2,300 transistors on a 14 mm2 die, multiplexed buses, and a clock frequency of just 740khz, all crammed into a 16-pin dual inline package, or DIP (it was the only IC package on hand at Intel in 1971). The 4004 employed a cutting-edge, 10 μm silicon-gate, PMOS process technology with enhancement loads fabricated on 2-inch wafers.
The Intel 4004 compared with the Intel Pentium Pro on the cover of the 1996 Microprocessor Forum portfolio celebrating the 25th anniversary of the microprocessor.
Back in the 1970s, we weren’t talking instructions per cycle (IPC), but rather cycles per instruction. Each 4004 instruction could be one or two bytes long. The 4004-instruction set consists of only 46 instructions: 41 were 8 bits wide and 5 were 16 bits wide. The instructions included data moving instructions, arithmetic operations, logic, rotate, control transfer, input/output, and some miscellaneous instructions. (Note: The Intel 4004 only had a 4-bit data bus, so even 8-bit instructions required two cycles to load.)
The chip was tiny by today’s standards, but it started the development of microprocessors and eventually changed the way people work, live and play. The 4004 was quickly followed by the 4040 and the 8008. But when Intel demultiplexed the address and data buses in the 40-pin DIP package of the 8080, the real microprocessor and personal computer business was started.
On a personal note, the 4004 is also the first microprocessor I learned to program. I know that ages me, but it was also the inspiration for my career in electronics. And by programming, I mean machine language — binary coding of the instructions like cavemen. The 4004 didn’t have a development board when it was announced, so my college professors designed their own single board computer.
While crude, the board was good enough for undergrads to learn the basics of microprocessors. The board allowed you to load binary data into memory using a makeshift hexadecimal keypad. You set the address with the hex keypad as well. When all the program bytes were loaded, you set the address back to 000 (12-bit addresses) and hit “run” to run the program. This same boot process was used by many early computers.
While I dabbled in RF and analog designs in college and after, the microprocessor captivated me back then and become the touchstone of my career. And it all started with the 4004, 50 years ago this week.