Question 1

How do I convert octal to decimal manually?

Accepted Answer

Multiply each digit by 8 raised to its positional power and sum the results. Example: octal 157 = (1×8²) + (5×8¹) + (7×8⁰) = 64 + 40 + 7 = 111 decimal.

Question 2

Why does octal use only digits 0–7?

Accepted Answer

Octal is base-8, so it uses exactly 8 symbols (0–7). The digit 8 and 9 do not exist in octal. Entering 8 or 9 in an octal number is invalid — similar to how binary only uses 0 and 1.

Question 3

What is the largest 3-digit octal number in decimal?

Accepted Answer

The largest 3-digit octal number is 777, which equals 7×64 + 7×8 + 7×1 = 448 + 56 + 7 = 511 decimal. This is why Unix permissions max out at 777 — 3 bits (read=4, write=2, execute=1) per permission group.

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