The physical socket on the motherboard that the CPU plugs in to. Different CPU families need different sockets, all incompatible shapes and sizes.

| Socket 462 (aka Socket A) | AMD Duron and Athlon | Socket 754 | AMD Athlon 64 | Socket 940 | AMD Athlon Opteron | Slot 1 | Intel Pentium II, III and Celeron (233-650MHz?) | Slot 2 | Intel Pentium II and Pentium III Xeons | Socket 7 | Intel Pentium | Socket 370 | Pentium III and Celeron ? | Socket 603 | Intel Pentium 4 Xeon | Socket 604 | Second generation Intel Pentium 4 Xeons, backwards compatible with 603 chips

Notes

1. for the sockets, the number generally refers to the number of pins on the CPU.
2. Socket 370 to Slot 1 adapters exist.