Socket 478

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Specifications
Socket 478

Type	PGA-ZIF
Chip form factors	Flip-chip pin grid array (FC-PGA2 or FC-PGA4)
Contacts	478 (not to be confused with the new Socket P that also uses 478-pins)
Bus Protocol	AGTL+
FSB	400 MT/s 533 MT/s 800 MT/s
Voltage range
Processors	Intel Pentium 4 (1.4 - 3.4 GHz) Intel Celeron (1.7 - 2.8 GHz) Celeron D (2.13 - 3.2 GHz) Intel Pentium 4 Extreme Edition (3.2, 3.4 GHz)
This article is part of the CPU socket series

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 supported only 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 3.2 GB/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.

While the original 400 MT/s bus matched the data rate of PC3200, this bus speed was already outdated by the time PC3200 became available. Dual-channel memory was introduced on later chipsets, so that a matched pair of PC3200 modules was able to match the final 800 MT/s FSB.

Celeron Ds are also available for Socket 478 and are the only CPUs still made for the socket. They use a quad-pumped 133 MHz bus giving a 533 MT/s FSB. They are available with 256 KB L2 Cache and are built on the 90 nm manufacturing process, using the Prescott core.

While the Intel mobile CPUs are available in 478-pin packages, they in fact only operate in a range of slightly differing sockets, Socket 479, Socket M, and Socket P, which are also incompatible with each other.

[edit] Socket 478 mechanical load limits

All socket 478 processors (Pentium 4 and Celeron) have the following mechanical maximum load limits which should not be exceeded during heatsink assembly, shipping conditions, or standard use. Load above those limits will crack the processor die and make it unusable.