Memory is measured in bytes.
A byte is 8 bits.
Two bytes are called a word.
Two words are called a double word which is 4 bytes (32-bit).
A quad word is eight bytes (64-bit).
A byte is 8 bits and is 2^8 power which is 256. The number of binary numbers in 8 bits in size is one of 256 values starting at 0 and going to 255.
Every byte of memory in a computer has its own unique address.