Octal
100
Octal System Guide
Octal Number System
The octal system uses 8 digits: 0-7. Each octal digit represents exactly 3 binary bits. That's why 64₁₀ = 100₈. Historically used in UNIX/Linux file permissions (chmod 755 = rwxr-xr-x) and memory addressing in older 8-bit systems.
File Permissions in Linux
Linux access rights (chmod) use 3 octal digits: owner, group, others. Each digit is the sum of permissions: read=4, write=2, execute=1. For example chmod 755 = rwxr-xr-x (7=r+w+x, 5=r+x, 5=r+x). chmod 644 = rw-r--r--.
Practical Applications
File permissions: chmod 400 (read only), chmod 755 (full), chmod 600 (private). Used rarely in Python and Java. In older IBM System/360 used for disk addressing. Conversion: 64₁₀ = 100₈, 255₁₀ = 377₈.