LGA 775, also known as Socket T, is an Intel desktop CPU socket. LGA stands for land grid array. Unlike earlier common CPU sockets, such as its predecessor Socket 478, the LGA 775 has no socket holes; instead, it has 775 protruding pins which touch contact points on the underside of the processor (CPU).
The Prescott and Cedar Mill Pentium 4 cores, as well as the Smithfield and Presler Pentium D cores, used the LGA 775 socket. In July 2006, Intel released the desktop version of the Core 2 Duo (codenamed Conroe), which also uses this socket, as does the subsequent Core 2 Quad. Intel changed from Socket 478 to LGA 775 because the new pin type offers better power distribution to the processor, allowing the front side bus to be raised to 1600 MT/s. The 'T' in Socket T was derived from the now cancelled Tejas core, which was to replace the Prescott core. Another advantage for Intel with this newer architecture is that it is now the motherboard which has the pins, rather than the CPU, transferring the risk of pins being bent from the CPU to the motherboard.
The CPU is pressed into place by a "load plate", rather than human fingers directly. The installing technician lifts the hinged "weld plate", inserts the processor, closes the load plate over the top of the processor, and pushes down a locking lever. The pressure of the locking lever on the load plate clamps the processor's 775 copper contact points firmly down onto the motherboard's 775 pins, ensuring a good connection. The load plate only covers the edges of the top surface of the CPU (processor heatspreader). The center is free to make contact with the cooling device placed on top of the CPU.
An examination of the relevant Intel data sheets shows that LGA 775 which is used for consumer level desktops and LGA 771 used for (Xeon based) workstation and server class computers appear to differ only in the placement of the indexing notches and the swap of two address pins. Many pins devoted to functions such as interfacing multiple CPUs are not clearly defined in the LGA 775 specifications, but from the information available appear to be consistent with those of LGA 771. Considering that LGA 775 predated LGA 771 by nearly a year and a half, it would seem that LGA 771 was adapted from LGA 775 rather than the other way around.
The socket was superseded by the LGA 1156 (Socket H) and LGA 1366 (Socket B) sockets.