# HAL 9000 and the Sexadecimal Mystery - Finally Explained! | Summary and Q&A

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September 7, 2021
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Dave's Garage
HAL 9000 and the Sexadecimal Mystery - Finally Explained!

## TL;DR

Sexadecimal is a numbering system used in early computers like the ORDVAC and ILLIAC, chosen to minimize the number of bits needed to represent a digit on their paper tapes, resulting in efficient encoding and compatibility with the hardware.

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### Q: Why did they choose the letters KSNJFL for the sexadecimal numbering system?

The specific reason behind choosing the letters KSNJFL for the sexadecimal numbering system remains unclear. One speculation is that it might have been done to distribute the letters across the hammer set of the Friden Flexowriter typewriter more evenly, reducing the risk of hammer jams. However, further research or insights from the community could provide more definitive answers.

Sexadecimal and hexadecimal are similar numbering systems, but they differ in the set of digits used. Hexadecimal uses the digits 0-9 and the letters A-F, while sexadecimal uses the digits 0-9 and the letters KSNJFL. Sexadecimal was chosen for its efficiency in representing digits with only four bits, making it advantageous for encoding data on the paper tapes used in early computers.

### Q: What is the significance of the ORDVAC and ILLIAC computers in relation to sexadecimal?

The ORDVAC and ILLIAC computers were early examples of machines that used the sexadecimal numbering system. They were part of the lineage of computers that adopted the von Neumann architecture, which is the foundation of modern computer systems. The use of sexadecimal in these computers allowed for efficient encoding on their paper tapes and compatibility with the hardware at the time.

### Q: How does sexadecimal make use of the high bit in the character encoding?

Sexadecimal makes use of the high bit in the character encoding by assigning it to control codes such as delay, newline, and carriage return. Since the high bit is never set for binary sexadecimal data, it can be used to signal control codes without interfering with the representation of digits. This allowed for the interspersing of control codes and data on the paper tapes, providing flexibility in data storage and communication.

## Summary & Key Takeaways

• HAL, the famous computer in 2001: A Space Odyssey, was programmed in sexadecimal.

• The ORDVAC and ILLIAC computers, which are part of the early computer lineage, were programmed in sexadecimal because it allowed for efficient encoding on their paper tapes.

• Sexadecimal is a numbering system that uses the digits 0-9 and the letters KSNJFL, allowing for simple representation of digits with only four bits.