1 byte comprises 8 bits
       can be represented as an ASCII character (or extended)
       can be represented as 2 hex digits (00 to FF) *****
       can have value 0 to 255  (0 to 2⁸-1)
       comprises 2 nibbles

1 nibble comprises 4 bits
         can be represented as 1 hex digit (0 to F)
         can have value 0 to 15 (0 to 2⁴-1)

1 bit can have value 0 to 1 (0 to 2¹-1)

Everything your computer is bytes.
Everything your disk     is bytes.
Everything your network  is bytes.

byte is the smallest data type in C.
byte is the smallest data type you can operate on directly.

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Do #1 (top part) only.

uchar is a commonly used alias for unsigned char.
 ^^^^

typedef  unsigned char  uchar