How are Signed integers different from unsigned integers once compiled? I alread

Question

How are Signed integers different from unsigned integers once compiled?

I already know about twos compliment and the like but my question is how can you tell the difference when looking at 8 bit integers when in binary eg 10000001 if this is a signed integer it would be equal to -127 but if it is unsigned it would be equal to 129. So my question is how can you tell the difference when presented with just 8 binary bits.

And also how are signed integers different from a compilers perspective, and how can a CPU tell the difference while performing arithmetic on them

Explanation / Answer

For simple types, you can't tell by looking at the bits in memory. Because the source specifies that the data is of a particular type, the compiler generates code that interprets the bits in memory as representing data of that particular type. In particular, in cases where different CPU instructions are needed (e.g., integer vs floating point), the compiler will generate instructions appropriate for the datatype in question. Note that, by the magic of two's complement, signed and unsigned integers are added, subtracted and multiplied by the same instructions. (That is, if you compute z=x

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