111111111001

111111111001 is a binary numeral consisting of twelve bits. As written, it is 111111111001 in binary. Interpreted as an unsigned value, it equals 4089 decimal and 0xFF9 in hexadecimal.

If interpreted as a 12-bit two's-complement signed integer, its value is -7.

The high-order portion is nine consecutive ones, followed by 0,0,1. It lies near the maximum 12-bit value of 4095 (0xFFF).

In early computing, 12-bit word sizes were used by devices such as the PDP-8 and some microprocessors, so strings like 111111111001 could appear in address or data examples.

In educational contexts, this pattern is used to illustrate binary arithmetic, bit masking, overflow, and wraparound behavior in fixed-width integers.

See also the Binary numeral system, two's complement representations, PDP-8, and 12-bit architectures.