Hexadecimal

Hexadecimal is a base 16 numbering system that uses sixteen symbols: the digits 0 through 9 and the letters a through f. One hexadecimal character encodes exactly four bits of data, so two characters represent one byte, which makes hex a compact, human readable way to write binary values.

How it works

Counting in hex runs 0 through 9, then a (ten) through f (fifteen), then 10, which equals sixteen in decimal. Because conversions between hex and binary are trivial, programmers use hex wherever raw data must be displayed. In bitcoin, transaction IDs and block hashes are 256-bit values shown as 64 hexadecimal characters, and a raw private key is likewise 64 hex characters. The famous leading zeros on block hashes, such as the genesis block hash beginning 000000000019d6, are the visible evidence of proof of work: a valid hash must fall below the difficulty target, which forces those zeros.

Why it matters

Anyone auditing bitcoin eventually reads hex, whether checking a transaction ID on a block explorer, comparing a software release hash against a signed checksum, or inspecting a raw transaction. Understanding that these strings are just large numbers in compact form demystifies much of the system. It also clarifies scale: a 64-character hex string represents a number up to 2 to the power of 256, and the practical impossibility of guessing such a number is the entire basis of bitcoin key security. Gold's security rests on atoms being hard to fake; bitcoin's rests on numbers this large being impossible to guess.