LGA 775

LGA 775
Type	LGA
Chip form factors	Flip-chip land grid array
Contacts	775
FSB protocol	AGTL+
FSB frequency	133 MHz (533 MT/s); 200 MHz (800 MT/s); 266 MHz (1066 MT/s); 333 MHz (1333 MT/s); 400 MHz (1600 MT/s)
Processor dimensions	1.47 × 1.47 inches (37.5mm)
Processors	Intel Pentium 4 (2.60 - 3.80 GHz); Intel Celeron D (2.53 - 3.60 GHz); Intel Pentium 4 Extreme Edition; (3.20 - 3.73 GHz); Intel Pentium D (2.66 - 3.60 GHz); Pentium Extreme Edition; (3.20 - 3.73 GHz); Pentium Dual-Core (1.40 - 3.33 GHz); Intel Core 2 Duo (1.60 - 3.33 GHz); Intel Core 2 Extreme (2.66 - 3.20 GHz); Intel Core 2 Quad (2.33 - 3.00 GHz); Intel Xeon (1.86-3.40 GHz); Intel Celeron (1.60 - 2.40 GHz)
Predecessor	Socket 478
Successor	LGA 1156; LGA 1366
	This article is part of the CPU socket series

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).^[2]

The socket was superseded by the LGA 1156 (Socket H) and LGA 1366 (Socket B) sockets.

Technical specifications

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 processor Core 2 Duo (codenamed Conroe), which also uses this socket, as does the subsequent Core 2 Quad.^[3] 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 installer lifts the hinged "load 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 socket's 775 pins, ensuring a good connection. The load plate only covers the edges of the top surface of the CPU (integrated heat spreader). 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) intel 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. In fact, using an adapter does allow LGA 771 processors to be used with LGA 775 motherboards.^[4]

Chipsets

Intel from i845 to 4X chipset:
i845GV/GE/i848P/i865G/GV/P/PE/i910GL/i915G/GL/GV/P/PL/i925X/XE/i945/955/i945G/P/ i955X/i946/946GZ/PL/965/i975/Q965/P965/G965/Q963/i975X/ X35/P35/Q35/G35/P33/G33/Q33/P31/G31/X38/X48/P45/P43/G45/G43/G41/B43/Q43/Q45,

SiS:
SiS 649/649FX/655/656/656FX/662/671/671FX/671DX/672

VIA:
PT800/PM800/PT880/PM880/P4M800/P4M800 Pro/PT880 Pro/PT880 Ultra/PT894/PT894 Pro/P4M890/PT890/P4M900

Ati:
ATI Radeon Xpress 200; ATI Radeon Xpress 1250, ATI CrossFire Xpress 3200

nVidia:
nForce4 Ultra; nForce4 SLI XE; nForce4 SLI; nForce4 SLI X16; nForce 570 SLI; nForce 590 SLI; nForce 610i; nForce 630i; nForce 650i Ultra; nForce 650i SLI; nForce 680i LT SLI; nForce 680i SLI; nForce 730i; nForce 740i SLI; nForce 750i SLI; nForce 760i SLI; nForce 780i SLI; nForce 790i SLI; GeForce 9300; GeForce 9400

Sources:^[5]

Improvements in heat dissipation

The force from the load plate ensures that the processor is completely level, giving the CPU's upper surface optimal contact with the heat sink or cold-water block fixed onto the top of the CPU to carry away the heat generated by the CPU. This socket also introduces a new method of connecting the heat dissipation interface to the chip surface and motherboard. With LGA 775, the heat dissipation interface is connected directly to the motherboard on four points, compared with the two connections of the Socket 370 and the "clamshell" four-point connection of the Socket 478. This was done to avoid the reputed danger of the heat sinks/fans of pre-built computers falling off in transit. LGA 775 was announced to have better heat dissipation properties than the Socket 478 it was designed to replace, but the Prescott core CPUs (in their early incarnations) ran much hotter than the previous Northwood-core Pentium 4 CPUs, and this initially neutralized the benefits of better heat transfer. However, modern Core 2 processors run at much lower temperatures than the Prescott CPUs they replace.

LGA 775 mechanical load limits

All LGA 775 processors have the following mechanical maximum load limits which should not be exceeded during heat sink assembly, shipping conditions, or standard use. Load above those limits will crack the processor die and make it unusable.

Location	Dynamic	Static
IHS Surface	756 N (170 lb_f) (77 kp)	311 N (70 lb_f) (31 kp)

The transition to the LGA packaging has lowered those load limits, which are smaller than the load limits of Socket 478 processors but they are bigger than Socket 370, Socket 423 and Socket A processors, which were fragile. They are large enough to ensure that processors will not crack.

LGA 775 Compatibility

Compatibility is quite variable, as earlier chip sets (Intel 915 and below) tend to support only single core P4 architecture CPU at 533/800 MT/s. Intermediate chip sets (e.g. Intel 945) commonly supported P4 dual core. For other chip sets, it also varies, as it is a complex issue of chip set capability, voltage regulator limitations and BIOS support.

Newer motherboards generally support all previous LGA 775 CPUs, but older boards may not support more recent CPUs

References

^ "Intel Pentium 4 Datasheet" (PDF). Archived from the original (PDF) on February 24, 2008.
^ "New P4 Socket Type LGA 775 (Socket T)". asisupport.com. Archived from the original on December 13, 2007. Retrieved 2007-03-14.
^ "Socket 775 / Socket LGA775 / Socket T". CPU World. Retrieved October 1, 2015.
^ "[MOD] LGA775 Support For LGA771 Xeon CPUs". Overclock.net. Retrieved March 23, 2015.
^ "ASRock > Motherboard Series". ASRock. Archived from the original on 15 March 2015. Retrieved 15 March 2015.

[1] "Intel Pentium 4 Datasheet" (PDF). Archived from the original (PDF) on February 24, 2008.

[2] "New P4 Socket Type LGA 775 (Socket T)". asisupport.com. Archived from the original on December 13, 2007. Retrieved 2007-03-14.

[3] "Socket 775 / Socket LGA775 / Socket T". CPU World. Retrieved October 1, 2015.

[4] "[MOD] LGA775 Support For LGA771 Xeon CPUs". Overclock.net. Retrieved March 23, 2015.

[5] "ASRock > Motherboard Series". ASRock. Archived from the original on 15 March 2015. Retrieved 15 March 2015.

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