Socket 370

Socket 370 is a CPU socket originally created for the Intel Celeron CPU. Having the cache integrated on-die obviated the need for the relatively expensive Slot 1 packaging. Socket 370 Celerons were originally released in early 1999 at 366 and 400 MHz, and could be plugged into a Slot 1 motherboard with an inexpensive adapter called a 'slotket'. Outside of the motherboard interface, they had the same capabilities as the Slot 1 versions of the same processor. This generation of Celerons was used in Abit's infamous BP6 dual-processor motherboard.

When the Coppermine core Pentium III was introduced in late 1999, it too integrated the cache on die. Thus, it too transitioned to the Socket 370 interface, but in a variant incompatible with previous Socket 370 motherboards. To distinguish between the two variants, the original Socket 370 chips were designated as PPGA (Plastic Pin Grid Array) and the newer ones as FC-PGA (Flip-Chip Pin Grid Array), the latter referring to the placement of the processor die on top of the package rather than on the bottom as was previously customary. Newer FC-PGA motherboards were, however, compatible with the older PPGA CPUs.

The VIA Cyrix III series of CPUs also used the Socket 370 interface, and were fully compatible with FC-PGA and newer S370 motherboards. It remained on Socket 370 for a while after Intel had effectively abandoned it, but the Cyrix processor line eventually switched to the Pentium 4's Socket 478.

Unfortunately, with the introduction of the Tualatin Pentium III and Tualatin Celeron in 2001, Intel created yet another non-backwards-compatible form of Socket 370, FC-PGA2. This difference required that a new chipset revision be used for the Tualatin, such as the i815 B-Step. This seriously annoyed Pentium III users who thought that the Tualatin would be a (relatively) inexpensive performance boost while waiting for the Pentium 4 to come down in price.

Compare these incompatibilities to the difference between the Thunderbird and Palomino Athlons, which on motherboards supporting a 133 MHz FSB required only a BIOS update.