Socket 478 was used by Socket 478 Celeron, Socket 478 Celeron D, Socket 478 Pentium 4 and Socket 478 Pentium 4 Extreme Edition CPUs. Keep in mind that these CPUs are available for other sockets as well, so we are talking specifically about socket 478 models here. In order to know what is the fastest CPU you can install on your motherboard, you will need to know what is the maximum FSB clock rate your motherboard supports. Typical values are 400 MHz, 533 MHz, 800 MHz and 1,066 MHz.

To make things simpler, we compiled the table below. At one side you have your motherboard FSB and on the other which CPUs are supported. Pay attention because some newer motherboards supporting 533 MHz and above can’t provide a 400 MHz FSB. You need to check on your motherboard manual if this is your case – if it is, your motherboard doesn’t support the installation of Socket 478 Celeron CPUs.

FSB	Celeron	Celeron D	Pentium 4	Pentium 4 Extreme Edition
400 MHz	All socket 478 models, available up to 2.8 GHz.	Not supported.	All socket 478 models up to 2.20 GHz and the 2.50 GHz model. There are also 2.40 GHz, 2.60 GHz and 2.80 GHz models using a 400 MHz FSB, but be careful as these models are also available for other FSB’s.	Not supported.
533 MHz	All socket 478 models, available up to 2.8 GHz.	All socket 478 models, available up to 3.2 GHz (“350” model). *	All socket 478 models up to 2.80 GHz and the 3.06 GHz model. Please be careful as there are 2.80 GHz, 2.60 GHz and 2.40 GHz versions also available for the 800 MHz FSB. *	Not supported.
800 MHz	All socket 478 models, available up to 2.8 GHz.	All socket 478 models, available up to 3.2 GHz (“350” model). *	All socket 478 models, available up to 3.4 GHz. *	All socket 478 models up to 3.4 GHz.
1,066 MHz	All socket 478 models, available up to 2.8 GHz.	All socket 478 models, available up to 3.2 GHz (“350” model).	All socket 478 models, available up to 3.4 GHz.	All socket 478 models, available up to 3.73 GHz.

* Not all motherboards support Celeron D and Pentium 4 CPUs based on “Prescott” core (all Socket 478 Celeron D CPUs are based on this core). This happens because of the new power specs required by Prescott-based CPUs. So take a careful look on your motherboard manual to find out if it supports Prescott-based CPUs (look for “Prescott” and “Celeron D” – if it supports Celeron D this means it supports Pentium 4 “Prescott” CPUs) or not. Here you can find a full list of Pentium 4 CPUs that are based on Prescott core, which may not work on older motherboards. On this same tutorial there is a list of Pentium 4 CPUs based on Willamette and Northwood cores, which work on all motherboards with the proper FSB.