About octal converter
Octal is base 8, using digits 0 to 7. Each octal digit equals three binary digits, so it is a compact way to write binary. For example 17 in octal is 15 in decimal.
Worked example
Unix file permissions use octal: each digit combines read (4), write (2) and execute (1). So 755 means the owner has 7 (4 + 2 + 1, full access) while the group and others have 5 (4 + 1, read and execute). And 644 is the usual setting for a normal file: the owner can read and write, everyone else can only read. To change 755 to binary, write each digit as three bits: 111 101 101.
How place values work
Each digit position is worth a power of the base. In decimal the places are 1, 10, 100, 1000 and so on. In binary they are 1, 2, 4, 8, 16, and in hexadecimal 1, 16, 256, 4096.
Why octal matters
- Computers store everything as binary; hexadecimal and octal are compact ways to write it.
- One hex digit equals exactly four binary digits, which is why programmers use it for colours, memory addresses and byte values.
- Octal groups three bits per digit and appears in Unix file permissions such as 755.
