The latest models of the Intel Celeron and Intel Pentium 4 use the LGA775 (also known as socket T) socket. The dual-core version of the Intel Pentium 4; the Intel Pentium D also fits into the same socket. To make things worse: Intel Core 2 Duo and Intel Core 2 Quad processors fit too!

All this can be confusing when upgrading or buying a new system. This article will explore the LGA775 socket and it’s possibilities.

Important!: Always check the product page of your boards manufacturer for compatibility!

What defines whether CPU x does run in LGA775 or not?


1. The chipset
2. The BIOS
3. The VRD

Important!: If one of these three factors are not applicable with your hardware the processor won’t be supported. Example: If your i915-based motherboard does support VRD10.1 and the BIOS supports the Intel Pentium D processor, the Intel Pentium D processor won’t work since the chipset is the limiting factor.

The chipset


The chipset on the motherboard is one of the three parts. Down below a short list of chipsets used on LGA775 boards with a LGA775 socket

ChipsetSupported CPU's
i865 / i875This chipset is rather old. Is able to run with the Intel Celeron, Intel Pentium 4, Intel Pentium D and Intel Core 2 Duo if the other two factors are positive.
i915This chipset is quite limited since it doesn’t support dual-core processors. That means only the Intel Celeron and Intel Pentium 4 are supported.
i925Intel Celeron, Intel Pentium 4.
i945Intel Celeron, Intel Pentium 4, Intel Pentium D (but not the D840 EE) and Intel Core 2 Duo
i955Intel Celeron, Intel Pentium 4, Intel Pentium D and Intel Core 2 Duo
i965Intel Celeron, Intel Pentium 4, Intel Pentium D, Intel Core 2 Duo and Intel Core 2 Quad.
i975Intel Celeron, Intel Pentium 4, Intel Pentium D, Intel Core 2 Duo and Intel Core 2 Quad.
nForce4Intel Celeron, Intel Pentium 4, Intel Pentium D (but not the D820), Intel Core 2 Duo.


The BIOS


The BIOS must be able to recognize the CPU. To check whether your BIOS is compatible with a specific processor please take a look at the product page of the manufacturer of your board since it's not possible to tell exactly which processor will run.

Basically and not always applicable: If your board supports a processor it's likely faster/slower processors will be supported too. But, watch out you're dealing with the same exact version (stepping).
Example: Four different versions of the 3GHz Intel Pentium 4 (Intel Pentium 4 530). The Intel Pentium 4 531 even exists in two models, the E0 and the G1.

The VRD


VRD stands for Voltage Regulation Down. In easy words this third part will be about delivering the correct voltage to your processor.

Basically I will discuss VRD10.1 and VRD11. The last one is required to run Intel Core 2 Duo processors. If your board (like the Intel D975X Rev. 0302 ‘Bad Axe’) does meet the first two requirements but doesn’t have the correct VRD version the CPU won’t run. Even if the BIOS will allow you to correct voltage settings manually!

VRD10.1 is needed for processors like the Intel Celeron, Intel Pentium 4 and Intel Pentium D. VRD11 is the minimum for Intel Core 2 processors. Of course it's backwards compatible which means that the 'VRD10.1'-processors will run with VRD11 too.

What is the difference between VRD10.1 and VRD11?

Both VRD10.1 and VRD11 are able to deliver voltages between 0.8375V and 1,6V. The big difference (which is actually small) can be seen in the steps between the voltages. VRD10.1 can take steps of 12.5mV. VRD11 is able to take smaller steps, namely 6.25mV.

Final words


Always check the product page of the manufacturer of your board. If you can't find a list of supported processors it's hard to tell whether a processor will function or not. If you can't find a list of supported processors check out if the chipset is compatible and search for information on the Internet. If you see someone on the Internet running an Intel Core 2 Duo E6300 you can be pretty sure an Intel Core 2 Duo E6400, E6600 and E6700 will run too as they are technically pretty much the same. Still be careful to check the technical specifications and be sure the FSB and stepping are the same.

22 April 2012 14:29

One of the best article I've ever red about cpus and motherboards. Thanks thandor. I know it's an old thread, but perhpas it has solved one of the most intriguing problem I met about this theme, because of my current motherboard: why not some cpu work on 4coredual-sata2 or p5vd1-x although they have the same features of othres similar processors. Ex. pentium ee 965.

p5vd1-x supports ee pentium processors supports also 1066mhz, supports pentium d also if only 800 but doesn't supports pentium ee 965 1066mhz ht dual core which presupposes the same vrd. So the solution is the chipset. Chipset is not compatible with this processor. The question is: how is it possible?

EDIT 24 april: I've just modified bios by P6 microcode of asrock conroe865pe, so to make the pentium ee 965 eventually recogniceble... or however I hope so.

This reply has been editted 2 times.

23 April 2012 11:21

Thanks!

I can't think of a reason it wouldn't work. The only major difference is that the Pentium Extreme Edition 955 and 965 come with Hyper Threading enabled. Yet the core (Presler) is identical to for example the Pentium D 960.

The older ASRock 775Dual-880Pro officially supports the 955 (check the CPU-support list). The 775Dual-880Pro can be (in my opinion) be considered as the first series of motherboards in the range from ASRock 775Dual-880Pro to 4CoreDual-VSTA and 4CoreDual-SATA2 R2.0 motherboards. They differ slightly in features, VRD, BIOS and chipset (PT880Pro ~ PT880Ultra including their south bridges).

Perhaps the Pentium Extreme Edition 955 and 965 will just work on the newer ASRock motherboards, or perhaps ASRock just didn't test these CPU's so they can't make sure it will work.

Unfortunately I don't own a Pentium Extreme Edition with Presler core so I can't test it.

22 May 2012 13:14

I've tested on P5VD1-X the pentium extreme edition 965 without result, so that the PC didn't start: NO POST.
That's very strange because P5VD1-X implements PT880ULTRA chipset
and I've modified BIOS replacing conroes865PE CPU microcode in the latest bios version...

Perhaps could be some PSU limitation and I'll rpeat the test with Thermaltake 750W thoughpower PSU hoping a different result.

This reply has been editted 1 time.

29 May 2012 20:11

I hope it will work with the stronger PSU. If not try resetting the BIOS to defaults. In case that doesn't help it might be worth a shot to use a working/compatible CPU and set the RAM ratio fixed so it will be easy going when the motherboard has to switch to 266MHz (1066) FSB.

03 June 2012 15:47

I've used the OCZ PSU 700W but i noted my OCZ PSUs (700w and 100w) have some kind of issues because of several problems implementing audiocards and videocars. So I will go to test my excewllent thermaltake thoughpower 750W PSU.
I thought what you suggested: to fix ddr value to 200mhz in order to avoid cpu fsb of 1066 could make 266mhz this value in bios settings.

This reply has been editted 2 times.

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