The first computers filled whole rooms, consumed as much electricity as a small town, and had less computing power than a modern musical greeting card. ENIAC (Electronic Numerical Integrator and Computer) is called the first general-purpose electronic digital computer. It was built at the University of Pennsylvania by J. Presper Eckert and John Mauchly for the US Army to calculate artillery firing tables, and was unveiled on 14 February 1946.
ENIAC (1946) — fact sheet
- Weight
- 27 tonnes (30 US short tons) — about 5 adult elephants
- Size
- 167 m² (1,800 sq ft) floor area; 2.4 m high, 0.9 m deep, 30 m long U-shaped row of 40 panels
- Power
- 150 kW — lights in Philadelphia reportedly dimmed when it was switched on
- Parts
- 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors, ~5 million hand-soldered joints
- Speed
- 5,000 additions or 357 multiplications or 38 divisions per second; 100 kHz clock
- Memory
- 20 accumulators of 10 decimal digits each (≈ 200 digits ≈ 80 bytes); no stored program
- Programming
- By re-plugging cables and setting 6,000 switches — took days. The 6 original programmers were women: Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas, Ruth Lichterman
- Reliability
- A tube failed roughly every 2 days; longest fault-free run ≈ 116 hours
- Cost
- $487,000 in 1946 (≈ $7–8 million today)
- Retired
- 2 Oct 1955 — ran 1946–1955 (in total ~70,000 hours)
Every unit of ENIAC and what it did
| Unit (count) | Job | Modern equivalent |
|---|---|---|
| Accumulators (20) | Each stored one 10-digit signed number and could add/subtract — the workhorse of the machine | Registers + ALU |
| Multiplier (1) | Used 4 accumulators to multiply two 10-digit numbers in 2.8 ms | Multiply unit in the ALU |
| Divider / Square-rooter (1) | Division and square roots by repeated subtraction | FPU |
| Master Programmer (1) | Controlled loops and sequencing — nested loops up to 10 levels | Control Unit / program counter |
| Cycling Unit (1) | Generated the 100 kHz pulses that kept every unit in step | Clock generator |
| Initiating Unit (1) | Start / stop / clear buttons; power sequencing | Power & reset button |
| Function Tables (3) | Read-only memory set by 1,200 ten-position rotary switches each — stored constants and tables | ROM / lookup tables |
| Constant Transmitter (1) | Fed numbers from punched cards into the machine | Input bus |
| IBM card reader & card punch | Input 125 cards/min; output 100 cards/min — results were printed later on an IBM tabulator | Keyboard / printer |
| Portable function table, 40 panels, 80 fans, cables & plugboards | Housing, cooling (room stayed at ~50 °C) and wiring | Cabinet, fans, motherboard traces |
Other early giants
| Machine | Year · Country | Technology | Weight / Size | Power | Speed | Note |
|---|---|---|---|---|---|---|
| Zuse Z3 | 1941 · Germany | 2,600 electromechanical relays | ~1,000 kg; 3 cabinets | 4 kW | add 0.8 s, multiply 3 s | First programmable automatic digital computer; destroyed in 1943 bombing |
| Atanasoff–Berry (ABC) | 1942 · USA | ~300 vacuum tubes, drum memory | ~320 kg; desk-sized | ~1 kW | 30 additions/s | First electronic digital computer (not programmable) |
| Colossus Mk 2 | 1944 · UK | 2,400 vacuum tubes | ~5 tonnes; 2.3 m × 5.2 m | 8.5 kW | 5,000 characters/s | Code-breaking; 10 built; secret till 1975 |
| Harvard Mark I | 1944 · USA | 3,300 relays, 765,000 parts | 4.3 tonnes; 15.5 m long | 5 kW | 3 additions/s; multiply 6 s | Programmed with paper tape; ran 15 years |
| ENIAC | 1946 · USA | 17,468 vacuum tubes | 27 tonnes; 167 m² | 150 kW | 5,000 additions/s | First general-purpose electronic computer |
| Manchester Baby (SSEM) | 1948 · UK | 550 tubes, Williams-tube memory | ~1 tonne; 5.2 m long | 3.5 kW | 1,100 instructions/s | First STORED-PROGRAM computer (21 June 1948) |
| EDSAC | 1949 · UK | 3,000 tubes, mercury delay lines | ~2 tonnes | 11 kW | 650 instructions/s | First practical stored-program machine |
| UNIVAC I | 1951 · USA | 5,200 tubes, mercury memory | 13 tonnes; 35 m² | 125 kW | 1,905 operations/s | First commercial computer in USA; 46 sold |
| IBM 650 | 1954 · USA | 2,000 tubes, magnetic drum | ~900 kg per unit | ~18 kW | ~1,000 ops/s | First mass-produced computer (~2,000 built) |
| TIFRAC | 1956 · India | 2,700 tubes | Room-sized | — | — | India's first indigenous computer (TIFR, Bombay); named by Nehru in 1962 |
| Apollo Guidance Computer | 1966 · USA | 2,800 ICs (first IC computer) | 32 kg; 61 × 32 × 17 cm | 55 W | 2.048 MHz; 4 KB RAM, 72 KB ROM | Took humans to the Moon |
Then vs now — the scale of progress
| Measure | ENIAC (1946) | Smartphone (2026) | Change |
|---|---|---|---|
| Weight | 27,000 kg | ≈ 0.19 kg | 140,000× lighter |
| Switching elements | 17,468 vacuum tubes | ≈ 20,000,000,000 transistors | 1,000,000× more |
| Additions per second | 5,000 | ≈ 2,000,000,000,000 (2 TFLOPS+) | 400 million× faster |
| Memory | ≈ 80 bytes | 12 GB RAM + 256 GB storage | 3 billion× more |
| Power | 150,000 W | ≈ 5 W | 30,000× less |
| Price (today's money) | ≈ $7 million | ≈ $300–1,000 | 10,000× cheaper |
Exam tip: ENIAC = Electronic Numerical Integrator And Computer; EDVAC = Electronic Discrete Variable Automatic Computer; EDSAC = Electronic Delay Storage Automatic Calculator; UNIVAC = UNIVersal Automatic Computer; ABC = Atanasoff–Berry Computer.
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