In signed 2's compliment architectures (primarily any microprocessor made in the mid 70s or later) that has flags (some RISC based CPUs, like the MIPS, don't have individual flags) will usually have an Overflow flag, (O or V), a Carry flag (C), a Zero flag (Z) and a Sign or Negative flag (S or N---here I'll be using N and V since I have a preference for Motorola CPUs). Yes, internal, a comparison is typically done via a subtraction; the flags are updated, but not the destination register. Now, depending upon how you want to interpret the results, as a signed comparison or unsigned comparison, depends on the flags you check (and the conditional jump (or branch) instructions will do this check for you). The flags that are checked for unsigned comparison are (!f means NOT f, i.e. the flag is not set):

    above or equal: !C
    above:          !C and !Z
    below or equal: C or Z
    below:          C

And the signed comparisons are:

    above or equal: N == V
    above:          N == V and !Z
    below or equal: N != V or Z
    below:          N != V

And, just for completeness, for both signed and unsigned:

    equal:   Z
    unequal: !Z