Bi-endian processors can run in either big endian or little endian mode under software control. Sign-magnitude is the simplest method for representing signed binary numbers. Numbers are negated by complementing all bits. The ripple effect of adding the carry bit can almost double the time to do an addition. Negation of a negative number in two's complement representation is accomplished by complementing all of the bits and adding one.
Addition is performed by adding the two numbers as unsigned integers and ignoring the carry.
Two's complement is used in just about every binary computer ever made. Most processors have one more negative number than positive numbers. In unsigned representation, only positive numbers are represented. Instead of the high order bit being interpretted as the sign of the integer, the high order bit is part of the number. In the past, processors tended to have proprietary floating point formats, although with the development of an IEEE standard, most modern processors use the same format.