CPU Socket

A CPU socket or CPU slot is an electrical component that attaches to a printed circuit board (PCB) and is designed to house a CPU (also called a microprocessor). It is a special type of integrated circuit socket designed for very high pin counts. A CPU socket provides many functions, including providing a physical structure to support the CPU, providing support for a heatsink, facilitating replacement (as well as reducing cost) and most importantly forming an electrical interface both with the CPU and the PCB. CPU sockets can most often be found in most desktop and server computers (laptops typically use surface mount CPUs), particularly those based on the Intel x86 architecture on the motherboard.

Interface types

CPU socket structure is largely dependent on the packaging of the CPU it is designed to house. Most CPUs are based on the pin grid array (PGA) architecture in which short, stiff pins are arranged in a grid on the underside of the processor are mated with holes in the socket. To minimize the risk of bent pins, zero insertion force (ZIF) sockets allow the processor to be inserted without any resistance and then lock in place with a lever or latch mechanism.

As of 2007[update], land grid array (LGA) packages have started to supplant PGA with most modern CPU designs using this scheme. The term LGA "socket" is actually a bit of a misnomer. With LGA sockets, the socket contains pins that make contact with pads or lands on the bottom of the processor package. While not popular for many years, LGAs are not new, microprocessors since the mid-1990's have used them.

In the late 1990s, many x86 processors fit into slots, rather than sockets. CPU slots are single-edged connectors similar to expansion slots, into which a PCB holding a processor is inserted. Slotted CPU packages offered two advantages: L2 cache memory size could be packaged with the CPU rather than the motherboard and processor insertion and removal was often easier. However, they proved to have performance limitations and once it was possible to place larger cache memory directly on the CPU die the industry reverted back to sockets.

Function

A CPU socket is often made up of plastic, a metal lever or latch and metal contacts for each of the pins or lands on the CPU. Most packages are keyed to ensure the proper insertion of the CPU. CPUs with a PGA package are inserted into the socket and the latch is closed. This has the effect of physically securing and protecting the CPU as well as causing an electrical connection between all the CPU pins and the socket. In the case of LGA the CPU is placed onto the socket and a latch is closed over the CPU, securing it. Most CPU sockets are designed to support the installation of a heatsink. It must be able to protect the CPU from the weight of the heatsink (often very heavy in weight relative to the CPU) particularly during the installation and removal, but also ensuring the heatsink makes good thermal contact with the CPU.

CPU sockets provide an advantage over directly attaching CPUs to the PCB by making it easier to replace the processor in the event of a failure. The CPU is often the most expensive component in the system and the cost of a CPU socket is relatively low which makes this popular among computer system manufacturers.

The nature of a CPU socket requires it to not only make good electrical contact with the CPU, but must also be solderable to the PCB with which it interfaces.

List of sockets and slots

Many socket names containing three- or four-digit numbers represent the number of pins on the processor or socket.