# HP-65

> first programmable scientific handheld calculator; with RPN and magnetic card reader, produced by Hewlett-Packard from 1974

**Wikidata**: [Q220638](https://www.wikidata.org/wiki/Q220638)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/HP-65)  
**Source**: https://4ort.xyz/entity/hp-65

## Summary
The **HP-65** is the first programmable scientific handheld calculator, introduced by Hewlett-Packard in 1974. It features **Reverse Polish Notation (RPN)** and a built-in **magnetic card reader** for storing and loading programs, making it a groundbreaking tool for engineers, scientists, and early computer enthusiasts.

## Key Facts
- **First programmable handheld calculator**: Released in **1974** by Hewlett-Packard, the HP-65 was the first device of its kind to combine scientific functions with user programmability.
- **Reverse Polish Notation (RPN)**: Uses postfix notation for calculations, a hallmark of HP calculators that eliminates the need for parentheses in complex equations.
- **Magnetic card reader**: Allows programs and data to be stored on small magnetic cards, a novel feature for portable calculators at the time.
- **LED display**: Features a **seven-segment LED display** for clear numerical output.
- **Used by NASA**: Employed in the **Apollo–Soyuz** mission, demonstrating its reliability in critical applications.
- **Discontinued in 1976**: Succeeded by the **HP-67** (handheld) and **HP-97** (desktop with printer).
- **Notable user**: **Steve Wozniak**, co-founder of Apple Inc., used the HP-65 in his early engineering work.
- **Power options**: Includes a **rechargeable battery** and an **AC power connector** for continuous use.

## FAQs
### Q: What makes the HP-65 significant in calculator history?
A: The HP-65 was the **first programmable handheld calculator**, introducing features like **magnetic card storage** and **RPN** that set the standard for future scientific calculators.

### Q: How did the magnetic card reader work?
A: The reader could **write programs to and read from small magnetic cards**, allowing users to save and load calculations without manual re-entry.

### Q: Who used the HP-65 professionally?
A: **NASA** used it during the **Apollo–Soyuz** mission, and **Steve Wozniak** relied on it for early computing projects.

### Q: What replaced the HP-65?
A: Hewlett-Packard released the **HP-67** (1976), a more advanced handheld model, and the **HP-97**, a desktop version with a built-in printer.

### Q: What display technology did the HP-65 use?
A: It featured a **seven-segment LED display**, common in early digital calculators for its brightness and clarity.

## Why It Matters
The HP-65 revolutionized portable computing by bringing **programmability** to a handheld device, bridging the gap between simple calculators and early computers. Its **magnetic card system** allowed users to store and share programs, a precursor to modern data storage solutions. The adoption by **NASA** and influential engineers like **Steve Wozniak** underscored its reliability and versatility. As the first of its kind, the HP-65 paved the way for advanced scientific calculators and demonstrated the potential of portable, user-programmable devices in technical fields.

## Notable For
- **First programmable handheld calculator**: The HP-65 was the first device to combine scientific functions with user-written programs in a portable form.
- **Magnetic card storage**: Introduced removable magnetic cards for program storage, a groundbreaking feature for its time.
- **RPN (Reverse Polish Notation)**: Popularized postfix notation in calculators, improving efficiency for complex calculations.
- **NASA certification**: One of the few calculators approved for space missions, used in the **Apollo–Soyuz** program.
- **Influence on early computing**: Inspired engineers like **Steve Wozniak**, who integrated its concepts into early personal computers.

## Body
### Overview
The **HP-65** is a **programmable scientific calculator** manufactured by **Hewlett-Packard** and released in **1974**. It is recognized as the first handheld calculator capable of running user-written programs, making it a landmark in computing history.

### Technical Specifications
- **Display**: Seven-segment **LED display** for numerical output.
- **Input Method**: Uses **Reverse Polish Notation (RPN)**, which processes operations without parentheses by entering numbers first, followed by the operator.
- **Programmability**: Users could write and store programs on **magnetic cards**, which could be reused across devices.
- **Power**: Operated via a **rechargeable battery** or an **AC power adapter**.
- **Dimensions**: Compact and portable, designed for field use by engineers and scientists.

### Magnetic Card System
The HP-65’s **magnetic card reader** was a defining feature, allowing programs and data to be saved on small, thin plastic cards with a magnetizable layer. This innovation enabled:
- **Program storage**: Up to **100 program steps** could be saved on a single card.
- **Data portability**: Cards could be shared between users or devices.
- **Durability**: The cards were reusable and resistant to wear, suitable for professional environments.

### Usage in Space Exploration
NASA certified the HP-65 for use in the **Apollo–Soyuz Test Project (1975)**, where it performed calculations for orbital maneuvers. Its reliability in zero-gravity conditions demonstrated its robustness.

### Successors
The HP-65 was discontinued in **1976** and succeeded by:
- **HP-67**: An upgraded handheld model with improved magnetic card storage.
- **HP-97**: A desktop version featuring a built-in printer for hard-copy output.

### Cultural Impact
The HP-65 influenced early computer pioneers, including **Steve Wozniak**, who used it for engineering tasks before co-founding Apple. Its design and functionality set a precedent for future programmable calculators and portable computing devices.

## Schema Markup
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  "description": "First programmable scientific handheld calculator with RPN and magnetic card reader, produced by Hewlett-Packard from 1974.",
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  "datePublished": "1974",
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## References

1. Freebase Data Dumps. 2013