Here is a quick rundown of all the different sockets and slots for processors:

Socket 1
This is an old slot. Its found on 486 motherboards and supports 486 chips, plus the DX2, DX4 Overdrive. It contains 169 pins and operates at 5 volts. The only overdrive it will support is the DX4 Overdrive.

Socket 2
This Intel socket is a minor upgrade from the Socket 1. It has 238 pins and is still 5 volt. Although it is still a 486 socket and supports all the chips Socket 1 does, it has the minor addition of being able to support a Pentium OverDrive.

Socket 3
Another Intel socket, containing 237 pins. It operates at 5 volts, but has the added capability of operating at 3.3 volts, switchable with a jumper setting on the motherboard. It supports all of the Socket 2 processors with the addition of the 5×86. It is considered the latest of the 486 sockets.

Socket 4
We move into Pentium class machines with the Socket 4, by Intel. This socket has 273 pins. It operates at a whopping 5 volts. Due to this voltage and the lack of any multipliers, this socket basically had no where to go but the history books. It only supports the low-end Pentium 60-66 and the Overdrive because these chips are the only Pentiums operating at 5 volts. Beginning with the Pentium-75, Intel moved to the 3.3 volt chip.

Socket 5
This socket operates at 3.3 volts with 320 pins. It supports Pentium class chips from 75MHz to 133MHz. Newer chips will not fit because they need an extra pin. Socket 5 has been replaced by the more advanced Socket 7. There are socket converters out there that can allow you to run more modern socket 7 processors in these socket 5 sockets. While socket 7 processors are still old by today’s standards, these converters can allow you to get more life out of your socket 5 motherboard.

Socket 6
You might think this is a nice Pentium socket class, but it is meant for 486’s. It is only a slightly more advanced Socket 3 with 235 pins and 3.3 volt operation. This socket is forgotten. The market never moved to use it because it came out when 486’s were already going of out style and manufacturers couldn’t see pumping money into changing their designs for a 486.

Socket 7
Socket 7 was the most popular and widely used socket for quite awhile. It contains 321 pins and operates in the 2.5-3.3 volt range using a split voltage (different I/O voltage and core voltage). It supports all Pentium class chips, from 75MHz on up, MMX processors, the AMD K5, K6, K6-2, K6-3, 6×86, M2 and M3, and Pentium MMX Overdrives. This socket was the industry standard and was being used for sixth-generation chips by IDT, AMD and Cyrix. Intel, however, decided to abandon the socket for it’s sixth-generation lineup. Socket 7 boards incorporate the voltage regulator which makes voltages lower than the native 3.3 volt possible.

Socket 8
This is a high-end socket used for the Pentium Pro. It has 387 pins and operates at 3.1/3.3 volts. It is designed especially to handle the dual-cavity structure of the chip, so the socket is a bit longer than the others. It is more rectangular than other sockets, which are more square. Since Intel decided to move on to Slot 1, the Socket 8 is a sort of dead end unless you really want to use a Pentium Pro.

Slot 1
Intel completely changed the processor paradigm with this new format. Instead of the processor core being in a socketed package, Intel placed their 6th generation Pentium II onto a daughtercard. Whereas socket 7 boards typically had the L2 cache on the board itself, this daughtercard has the L2 cache on the card itself. This increases speed by allowing the processor to communicate quickly with the L2 cache without having to be limited to the speed of the system bus, as was the case with socket 7. Slot 1 itself has 242 pins and operates at 2.8-3.3 volts. The Slot 1 is used mainly for the P2,P3 and Celeron, but Pentium Pro users can use the slot by mounting their processors in a socket 8 on a daughtercard which is then inserted into the Slot 1. This converter gives Pentium Pro users the ability to upgrade later.

The release of this slot was mostly a competitive blow to AMD more than anything else. The socket designs previously used were not patented to be sure competitors could not use it. With the release of Slot 1, the wiring structure was patented so that no other manufacturer could use the design without approval from Intel. This is why we do not see any AMD processors making use of Slot 1. They had to create their own slot, slot A, to move onto the slotted interface.