CPU socket pins
Computer processors and motherboards are differentiated primarily by their CPU socket number. The CPU socket number is used to define the compatibility between different types of processing architectures, even within the same family of processor motherboard, for computer building purposes. Moreover, in many cases, the CPU socket number denotes cooling considerations that must be taken into account, and sometimes the physical characteristics of the CPU and socket itself.
Physical Characteristics
Though not an absolute rule, the CPU socket number is often a reference to the number of pins or contacts on the CPU itself that interface the processor and the motherboard. For example, Intel's LGA and socket 775 and socket 1366 have 775 and 1366 pins respectively that connect the CPU to the motherboard. The prefix to the CPU socket, such as LGA, refers to whether or not the pins are on the CPU or the motherboard itself. In the case of LGA, land grid array, the pins are actually on the motherboard, and small contacts are on the CPU that rests upon these pins.
Size Specifications
As the size of the CPU socket is directly proportional to the number of pins it possesses, the CPU socket number serves as a rough guide to the area where the CPU socket will reside. Though CPU processors are getting smaller, such as Intel's 32 nm technology, the connective sockets that connect the CPUs to the rest of the computer remain in standardized sizes and thus grow as the number of transistors and connections utilized by the CPU grows.
Cooling Considerations
CPU sockets not only define the specifications that facilitate communication between the CPU and the motherboard, but also the physical imprint on where the CPU socket resides. The pre-machined mounting terminals for cooling solutions such as air or water cooling apparatus is different for every CPU socket as each socket has different physical dimensions and requirements. Furthermore, high-performance sockets such as Intel's 1366, which have considerable thermal output, often take up larger portions of the motherboard to allow for larger and more complex cooling apparatus to be attached to the CPU. Cooling solutions are often sold according to what CPU socket they are compatible with, and are rarely compatible with non-listed sockets.
CPU Compatibility
CPU sockets only support a specific number of CPUs. Though more CPUs may be designed for them, such as Intel socket LGA 775, which supported several families of processors from the Celeron to the Core 2 Quad, once the maximum efficiency of a particular socket is reached it will be deprecated for a newer design. As such, when building computers the first piece of hardware chosen should be the motherboard based upon which CPU socket it possesses. This specification alone dictates which processors are supported for the new computing system.
LGA vs PGA
The three-letter prefix for every CPU socket number, either LGA or PGA, describes physical connective characteristics between the CPU and the motherboard. CPU socket numbers with the prefix LGA, or land grid array, are sockets containing contact pins that the CPU rests on. There is a small metal contact on the bottom of the CPU for every pin in the socket. PGA, also known as pin grid array, is the predecessor to LGA CPU socket configurations. That is to say, the connective pins are connected to the underside of the processor. Each of these pins fits into a small pre-machined hole within the CPU socket on the motherboard that holds the CPU pins in place.
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