Why hexadecimal notation is preferred to octal in computing?

JR answered your question here: "A 2 digits hex code is equivalent to one "byte" of 8 bits" So it's more convenient for representing the data sizes that most computers use. But his first sentence is wrong. Octal converts to binary just as effortlessly as hex, it's just 3 bits at a time instead of 4. e.g. the octal value 7531 is in binary 111 101 011 001

The standard computer word sizes are powers of 2 - 8, 16, 32, 64 bits. A hexadecimal value is a multiple of 4 bits, so it fits neatly into computer words. An octal value is a multiple of 3 bits thus does not neatly fit into computer words. Special routines are needed to handle octal values that are greater than the computer word size.