LGA 775

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LGA 775
CPU Socket 775 T.jpg
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)[1]
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The socket was superseded by the LGA 1156 (Socket H) and LGA 1366 (Socket B) sockets.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[edit]

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 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 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.

Chipsets[edit]

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/G35/P33/G33/Q33/P31/G31/X38/X48/P45/P43/G45/G43/G41,
all support LGA 775.

Improvements in heat dissipation[edit]

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[edit]

The LGA 775 contact points on the underside of a Pentium 4 Prescott CPU

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 lbf) (77 kp) 311 N (70 lbf) (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.

See also[edit]

References[edit]

  1. ^ "Intel Pentium 4 Datasheet". 
  2. ^ "New P4 Socket Type LGA 775 (Socket T)". asisupport.com. Retrieved 2007-03-14.