Why can't tinyint store more than the number 255 in MySQL?

Question

If TINYINT can store three characters, for example, why can't it store up to the number 999?

Answer 1

Because it takes only 8 bit and hence can encode no more than 2^8 = 256 values.

The three characters you see in something like '123' are the result of the binary to decimal conversion. You cannot store arbitrary 3 characters there.

Answer 2

It is 8 bits and can actually store a maximum value of 255. 8 bits have 256 possible states including zero.