Socket 1 169-pin Found on 486 motherboards, operated at 5 volts and supported 486 chips, plus the DX2, DX4 OverDrive.
Socket 2 238-pin A minor upgrade from Socket 1 that supported all the same chips. Additionally supported a Pentium OverDrive.
Socket 3 237-pin Operated at 5 volts, but had the added capability of operating at 3.3 volts, switchable with a jumper setting on the motherboard. Supported all of the Socket 2 chips with the addition of the 5x86. Considered the last of the 486 sockets.
Socket 4 273-pin The first socket designed for use with Pentium class processors. Operated at 5 volts and consequently supported only the low-end Pentium-60/66 and the OverDrive chip. Beginning with the Pentium-75, Intel moved to the 3.3 volt operation.
Socket 5 320-pin Operated at 3.3 volts and supported Pentium class chips from 75MHz to 133MHz. Not compatible with later chips because of their requirement for an additional pin.
Socket 6 235-pin Designed for use with 486 CPU's, this was an enhanced version of Socket 3 supporting operation at 3.3 volts. Barely used since it appeared at a time when the 486 was about to be superseded by the Pentium.
Socket 7 321-pin Introduced for the Pentium MMX, the socket had provision for supplying the split core/IO voltage required by this and later chips. The interface used for all Pentium clones with a 66MHz bus.
Socket 8 387-pin Used exclusively by the Intel Pentium Pro, the socket proved extremely expensive to manufacture and was quickly dropped in favour of a cartridge-based design.
Slot 1 242-way connector The circuit board inside the package had up to 512KB of L1 cache on it - consisting of two 256KB chips - which ran at half the CPU speed. Used by Intel Pentium II, Pentium III and Celeron CPUs.
Slot 2 330-way connector Similar to Slot 1, but with the capacity to hold up to 2MB of L2 cache running at the full CPU speed. Used on Pentium II/III Xeon CPUs.
Slot A 242-way connector AMD interface mechanically compatible with Slot 1 but which using a completely different electrical interface. Introduced with the original Athlon CPU.
Socket 370 370-pin Began to replace Slot 1 on the Celeron range from early 1999. Also used by Pentium III Coppermine and Tualatin CPUs in variants known as FC-PGA and FC-PGA2 respectively.
Socket A 462-pin AMD interface introduced with the first Athlon processors (Thunderbird) with on-die L2 cache. Subsequently adopted throughout AMD's CPU range.
Socket 423 423-pin Introduced to accommodate the additional pins required for the Pentium 4's completely new FSB. Includes an Integral Heat Spreader, which both protects the die and provides a surface to which large heat sinks can be attached.
Socket 603 603-pin The connector for Pentium 4 Xeon CPUs. The additional pins are for providing more power to future CPUs with large on-die (or even off-die) L3 caches, and possibly for accommodating inter-processor-communication signals for systems with multiple CPUs.
Socket 478 478-pin Introduced in anticipation of the introduction of the 0.13-micron Pentium 4 Northwood CPU at the beginning of 2002. It's micro Pin Grid Array (µPGA) interface allows both the size of the CPU itself and the space occupied by the socket on the motherboard to be significantly reduced.
Socket 754 754-pin AMD’s 754-pin CPU interface form factor introduced with its 64-bit Athlon 64 processor in the autumn of 2003.
Socket 939 939-pin AMD’s 939-pin CPU interface form factor introduced in the summer of 2004. The Socket 939 marked the convergence of the mainstream and FX versions of the Athlon 64 CPU, which had previously used different interfaces, the Socket 754 and Socket 940 respectively.
LGA775/
Socket T 775-pin Land Grid Array 775: Intel's proprietary CPU interface form factor introduced in the summer of 2004. Similar to a pin grid array (PGA), the connection between LGA775 chip packaging and the processor chip is via an array of solder bumps rather than pins.