Socket 478

In computing, Socket 478 is a type of CPU socket used for Intel's Pentium 4 and Celeron series CPUs. Socket 478 was phased out with the launch of LGA775.

Socket 478 has been used for all of the Northwood Pentium 4s and Celerons, the first Prescott Pentium 4s, and some Willamette Celerons and Pentium 4s. Socket 478 also supports newer Prescott Celeron Ds, and early Pentium 4 Extreme Edition processors with 2MB of L3 cache and some Core Duos. The socket was launched with the Northwood core to compete with AMD's 462-pin Socket A and their Athlon XP processors. Socket 478, which accommodates high and low-end processors, was also the replacement for Socket 423, a Willamette processor socket which remained in the market for only a short time.

Motherboards that use this socket support DDR, RDRAM, and in some cases SDRAM. However, the majority of boards are DDR based. Initial motherboards only supported RDRAM, however RDRAM is quite expensive, compared to DDR and SDRAM, and consumers demanded an alternative, thus DDR and SDRAM boards were made. Later revisions to chipsets that support Socket 478 added higher FSB speeds, higher DDR speeds, and support for dual channel DDR.

Like the previous Socket 423, Socket 478 is based on Intel's Quad Data Rate technology, with data transferring at four times the clock rate of its Front Side Bus. As such, the 400 MT/s bus was based on a 100 MHz clock signal, but was still able to provide 3.2GB/s of data to the chipset. At its release, no SDRAM product was capable of supporting so high a data rate, so Intel pushed forward RDRAM technology, with two channels of PC800 providing synchronous data capability. Poor consumer acceptance of expensive RDRAM lead Intel to release low-performance PC133-supporting chipsets, and finally DDR chipsets.