The '51 and 'S51 contain two independent 2-wide 2-input AND-OR-INVERT gates.
They perform the Boolean function Y = AB + CD\.
The 'LS51 contains one 2-wide 3-input and one 2-wide 2-input AND-OR-INVERT
gates. They perform the Boolean functions 1Y = (1A · 1B ·
1C) + (1D · 1E · 1F)\ and 2Y = (2A · 2B) +
(2C · 2D)\.
The SN5451, SN54LS51, and SN54S51 are characterized for operation over
the full military temperature range of -55°C to 125°C. The SN7451,
SN74LS51 and SN74S51 are characterized for operation from 0°C to 70°C.