Whatever Happened to Octal? A Brief History of a Forgotten Number Base
Published 2026-09-14
Octal's brief moment as the default
In the 1950s-70s, octal (base 8) was a genuinely common way for programmers to read and write raw computer data, particularly on machines built with word sizes that were multiples of 3 bits — 12-bit, 24-bit, and 36-bit architectures were common in that era, and octal divides those word sizes into neat, even groups (three binary digits per octal digit) the same way hexadecimal divides 8-bit and 16-bit words evenly today.
Why hexadecimal eventually won
As the computing industry standardized on 8-bit bytes and 16-, 32-, and 64-bit word sizes (all powers of two), octal's neat 3-bit grouping stopped lining up evenly, while hexadecimal's 4-bit grouping fit perfectly. By the 1980s, hex had almost completely replaced octal as the default "human-readable shorthand for binary" across the industry, and it's remained that way ever since.
Where octal quietly survives today
There's one place almost every developer still encounters octal directly: Unix and Linux file permissions. Running a command like chmod 755 script.sh is setting permissions using octal notation, where each digit (7, 5, 5) represents a combination of read, write and execute permissions for the file's owner, group, and everyone else, encoded as a sum of the values 4 (read), 2 (write), and 1 (execute). This system dates directly back to Unix's 1970s design and has simply never been replaced, because it works and changing it would break decades of scripts and documentation.
A quick permissions example
In chmod 755, the digit 7 (4+2+1) means "read, write and execute," while each 5 (4+1) means "read and execute, but not write." That's why 755 is such a common permission setting for executable scripts: the owner can edit and run it, while everyone else can only run it, not modify it.
Converting octal today
Outside of Unix permissions, you're unlikely to need octal for everyday work, but when you do encounter it, our Octal Converter converts it instantly to decimal, binary and hexadecimal, so you can double-check exactly what permission set (or other octal value) you're looking at.