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[[Category:Computer Architecture]]

A ''signed'' value is a binary value with a positive/negative ''sign''. Alternatively, an unsigned number can represent positive (or zero) values only.

Some number representations allow for both positive and negative zero values.

== Two's Compliment ==

In two's compliment integer representation, positive integer values are represented by the binary representation of the integer, and negative integer values are represented by the '''two's compliment''' of the absolute integer value -- effectively, (2<sup>'''width'''</sup>-abs('''n''')), where '''width''' is the word size in bits, and '''n''' is the integer being represented.

Example: A single unsigned [[Word#Byte|byte]] (8 bits) stores an integer value in the range of 0 to (2^8 - 1 =) 255. If the byte is treated as a signed value, then values from 0-127 (0x00-0x7F) are treated as the positive integers 0-127, and the values 128-255 (0x80-0xFF) are treated as negative integers -128 to -1.

Notice that in two's compliment representation, the highest-order bit is the sign bit: 0 == positive, 1 == negative.

Signed address offsets are often used for relative [[Addressing Mode|addressing modes]].

== BCD ==

In signed [[BCD]], the high-order nibble is used to represent the sign (0 == positive, non-0 == negative).