Intel's first Pentium 4 socket (423) was a temporary solution that has long since exited the market, but its second Pentium 4 socket (478) is still around, supporting processors from 1.6 GHz to 3.4 GHz. It has been replaced at the high-end by LGA 775, but is currently seeing resurgence at the low end due to low chipset prices and sub-$50 Celeron D processors. As such, it may still be an option for the most frugal buyers.

Compatibility issues start with early Socket 478 motherboards supporting no higher than 133 MHz bus processors (referred to as FSB533), to middle-era versions supporting 200 MHz/FSB800 bus processors, but only few 90 nm cores such as Prescott and its Celeron D variations. Once again, it's necessary to check the motherboard manufacturer's Website for CPU compatibility.

Socket 754 (AMD Athlon 64 And Sempron)

First to support AMD's modern Athlon 64 processors, Socket 754 supports a single-channel of DDR-SDRAM memory via its On-chip memory controller. The seemingly incredible increase in pin count is a result of the CPU being separately linked to both memory and the chipset, rather than accessing memory through the chipset. Sockets 754 and 939 were the first to replace the parallel processor bus by a serial interconnect (HyperTransport), with a 200 MHz base clock speed.

Prices under $50 for certain Sempron processor models make Socket 754 worthy of consideration for budget system builders, even though there won't be any new processor models for this socket.

Compatibility issues for Socket 754 motherboards are uncommon and limited to older BIOS revisions not supporting the latest processors. Incompatible matches will usually operate well enough to allow a BIOS update and add proper processor support, but it's still best to check the motherboard manufacturer's documentation.