What Is Socket 5?

Socket 5 was a specification that outlined the physical and electrical connection between a computer’s central processing unit (CPU) and motherboard. It was used in Intel® Pentium® processors during the mid 1990s and by competing companies that made Intel®-compatible processors. Socket 5 had 320 pins and was designed to deliver 3.3 volts of power to the CPU. Its successor, Socket 7, reused many elements of the Socket 5 design and enabled some degree of backward compatibility. Both platforms have been obsolete since the end of the 1990s, though replacement processors and motherboards can be found on auction sites and in surplus stores.

The CPU of a typical personal computer (PC) connects to a computer’s motherboard through a series of metal pins that carry electrical signals. These pins, located on the underside of a CPU, plug into a series of holes on the motherboard. The number, size, and arrangement of the pins and their corresponding holes are governed by CPU socket specifications. Companies that design and market CPUs set these standards, allowing a mix of different chips and motherboards to be used together as long as they are of the same socket type. Socket standards also specify the level of voltage to be delivered to the CPU.

The Socket 5 standard was created by Intel® in the mid 1990s for the second iteration of its Pentium® line of processors. Specifically, Pentium® processors running between 75 and 133 megahertz were supported, while earlier and later models used other types of sockets. Some of Intel’s competitors took advantage of the specification by selling lower cost, drop-in replacement chips that were Socket 5 compatible. The socket was roughly square with a staggered pin array, meaning that the pins were arranged in a diagonal pattern that allowed them to be spaced more closely together than previous layouts.

Socket 5 only lasted about a year before a replacement was released, but its layout and pin arrangement were reused for its successor, Socket 7. Socket 7 supported newer, dual voltage processors and introduced an extra “key pin” designed to prevent users from inserting a CPU upside down. These changes were minor enough that a Socket 5 CPU could be inserted in a Socket 7 motherboard. Adaptors to upgrade Socket 5 motherboards were also sold, allowing the newer Socket 7 processors to be used in motherboards using the older designs.