bit, byte, and word
Everything in a computer is built from the smallest possible answer to a yes-or-no question. A light switch is either on or off; a single bit is either 1 or 0. That is genuinely all a computer fundamentally stores — vast oceans of these tiny switches. Numbers, text, photos, and programs are all just patterns of bits, grouped and interpreted by agreement.
Bits are tiny, so we work in groups. A byte is a group of 8 bits, the standard small unit of memory; a single byte can take any of 2^8 = 256 different patterns, enough to stand for one text character or a small number. A word is the natural chunk a particular processor handles in one go — often 32 or 64 bits on modern machines. Word size is a key architectural number: a 64-bit machine moves and computes on 64-bit words at a time and can directly address an enormous range of memory, while an older 32-bit machine works in 32-bit words.
Getting these straight prevents endless confusion: network speeds are usually quoted in bits per second while file sizes are in bytes, so a number can look eight times off if you mix them up. And while a byte is universally 8 bits today, word size is not fixed across machines — it is a property of the architecture, which is exactly why the jump from 32-bit to 64-bit computing was such a big deal. Deeper encoding of numbers and text lives in the data-representation field; here we just need the vocabulary.
0b01000001 is one byte, eight bits. Read as a character code it is the letter A; read as a plain number it is 65. Same bits, different agreed interpretations — that flexibility is the whole point.
A bit is a switch, a byte is 8 of them, a word is what the machine handles at once.
A byte is 8 bits everywhere today, but word size is per-architecture (32 vs 64 bits matters). And bits-per-second versus bytes-per-second is a factor-of-eight trap worth memorising.