LGA 775 (land grid array 775), also known as Socket T, is an Intel desktop CPU socket. Unlike PGA CPU sockets, such as its predecessor Socket 478, LGA 775 has no socket holes; instead, it has 775 protruding pins that touch contact points on the underside of the processor (CPU). It is the last Intel socket that supports the front-side bus interface (FSB).
Intel started selling LGA 775 (Socket T) CPUs with the 64-bit version of their 90 nm "Prescott"-based Pentium 4 HT.
Improvements in heat dissipation
thumbnail|Intel [[Core 2 Duo E7500 2.93 GHz installed into LGA 775 socket]]
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 Socket 370 and the "clamshell" four-point connection of 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. Nonetheless, the later Core 2 processors run at much lower temperatures than the Prescott CPUs they replaced.
Processors with lower TDP and clock speeds only used Thermal Interface Compound in between the die and the integrated heat spreader (IHS), while processors with higher TDP and clock speeds have the die soldered directly to the IHS, allowing for better heat transfer between the CPU and the integrated heat spreader.
LGA 775 mechanical load limits
thumb|right|250px|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 that should not be exceeded during heat sink assembly, shipping conditions, or standard use. Load above those limits could crack the processor die and make it unusable. The limits are included in the table below.
{| class="wikitable" style="font-size: 95%; text-align: center;"
|-
! rowspan=1 style="width:12em" | Location
! rowspan=1 | Dynamic
! rowspan=1 | Static
|-
| IHS Surface
| 756 N (170 lb<sub>f</sub>) (77 kp)
| 311 N (70 lb<sub>f</sub>) (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 chipsets (Intel 915 and below) tend to support only single core NetBurst Pentium 4 and Celeron CPUs at an FSB of 533/800 MT/s.
Intermediate chipsets (e.g. Intel 945) commonly support both single core Pentium 4-based CPUs as well as dual core Pentium D processors. Some motherboards using the 945 chipset could be given a BIOS upgrade to support 65nm Core-based processors. Other chipsets have varying levels of CPU support, generally following the release of contemporary CPUs, as LGA 775 CPU support is a complicated mixture of chipset capability, voltage regulator limitations and BIOS support. For example, the newer Q45 chipset does not support NetBurst-based CPUs such as the Pentium 4, Pentium D, Pentium Extreme Edition, and Celeron D.
Virtualization capabilities
Some Core 2 and other LGA 775 processors are capable of hardware-accelerated virtualization. More recent hypervisors might not be compatible with these CPUs because they lack support for Extended Page Tables.
See also
- List of Intel processors
- List of Intel Pentium 4 processors
- List of Intel Core 2 processors
- List of Intel Xeon processors