Status registers are exactly what the name insinuates,
registers that dictate status. They're bloody
flags. Each processor has a set of 'em which can be interrogated by
machine language instructions. Ordinarily they're single
binary digits and a number of status registers will be contained within a single
register of, guess how many, yes, the magic number, 8
binary digits.
Examples would include the
carry flag, which is set if the addition of two digits causes a carry and a
zero flag is set if the compare instruction or arithmetic operation just executed gives a
zero result.