EM64T Information

I thought I'd prepare a thread on this, hopefully moderators will make it a sticky for the time being. I've noticed this comes up alot. So I will try to answer the standard questions all at once. I'll cover Prescott 64 bit compatibility and the Xeon processors as well.

Identifying an Intel 64bit processor.

Pentium 4 Prescott's with the "F" suffix are 64 bit compatible. Currently none are shipping in boxed form and they are only avialable to OEM's at the moment. (Someone correct me when or if this has changed) For example a Pentium 4 Model 550F is a 64 bit processor. While a 550J isn't. J denotes the EDB instruction. (Execute Disable Bit)

Xeon (Nacona) processors that have an 800MHz FSB all have EM64T.

Q: Is EM64T compatible with x86-64 instructions?

A: EM64T is Intel's implimentation, x86-64 is AMD's. While they are not exactly the same, for all intensive purposes they are compatible. According to Intel's site they will be perfectly compatible in most cases.

Q: Is it true 64 bit compatibility?

A: Yes. The processors can run "64bit" coded software. It is not emulation.

Q: What motherboard chipsets are required to use EM64T?

A: Motherboards must use the i925X or chipset for EM64T compatibility. Xeon's must have the i7525 Turnwater chipset in order to be compatible. No other chipsets are compatible. This information comes from Intel's chipset comparison guide and the current information on their site about the LGA775 Pentium 4 processors with the "F" suffix affixed to their name.

Q: Will the i925XE chipsets work with EM64T?

A: Intel's site does not specifically state it will or it won't. It only specifies that the i925X chipset will support EM64T.

Q: Will the i915x chipsets work with EM64T?

A: Intel's site does not specifically state it will or it won't. It only specifies that the i925X chipset will support EM64T.

Q: Will processors with EM64T be available in the Socket 478 platform?

A: The answer is no. Intel has stated that no new Pentium 4's will be made available in socket 478 form. Althought that may not apply to the Celeron's which I suspect won't gain EM64T instructions for quite some time. Probably not before the Celeron goes LGA775 only.

Q: If I have a Pentium 4 with EM64T and I install it in a i915x based motherboard, will it work?

A: There is no information on that I can find at this time. It may be that the processor will work, but the 64bit instructions will not work. This might be the case, as the voltages and thermal requirements for EM64T processors are the same.

Q: The i875P chipset supports 800MHz FSB's and Xeons. Can I use a 800MHz FSB Xeon (Nacona) in an older motherboard such as the Asus PC-DL?

A: No. the 800MHz FSB Nacona has different thermal requirements and power requirements due to the core change from a Prestonia/Gallatin core to a Prescott based core.

Q: Will boards like the AS8 that use the i865PE/i875P support the EM64T enabled Pentium 4?

A: No. These chipsets will not be compatible with EM64T processors.

Q: I've heard I need a special BIOS to use EM64T processors.

A: Motherboards released with supported chipsets, that were shipped out before validation of EM64T processor could occur will likely need a BIOS update. Motherboards released after a certain date should be fine right out of the box.

Q: Will Pentium 4's with EM64T support also include the EDB feature?

A: E0 stepping CPU's will feature both.

Q: When will EM64T processors be available in retail boxes?

A: Although I don't have a specific date, information gathered from Intel traning events tells me that the processors will start shipping to retail channels in Q1 2005. More than that I don't know.


That's all I can think of right now. If anyone has anything to add please feel free to mention it. Or ask any other related questions.

Just to add a few things.

1. AMD calls it the XD bit, Intel calls it the Execute Disable Bit (EDB).

2. The 6xx series P4's are based on the E0 stepping and will support EM64T. The E0 stepping includes, among other things, EDB functionality. The 6xx series P4's will be released at the end of February 2005.

3. AMD64 and EM64T are compatible, they must be. If they weren't, all software would have to be compiled into two separate versions, one for AMD CPUs and one for Intel CPUs.

4. The 'F' series P4's don't use the new naming scheme, such as 540, 550, etc. They use the GHz rating, i.e. 3.4F GHz. It is rumored Intel did this because they won't ever be offered in boxed, retail versions, only to OEMs for use in business workstations.

Originally Posted by DanIdentity

Just to add a few things.

1. AMD calls it the XD bit, Intel calls it the Execute Disable Bit (EDB).

2. The 6xx series P4's are based on the E0 stepping and will support EM64T. The E0 stepping includes, among other things, EDB functionality. The 6xx series P4's will be released at the end of February 2005.

3. AMD64 and EM64T are compatible, they must be. If they weren't, all software would have to be compiled into two separate versions, one for AMD CPUs and one for Intel CPUs.

4. The 'F' series P4's don't use the new naming scheme, such as 540, 550, etc. They use the GHz rating, i.e. 3.4F GHz. It is rumored Intel did this because they won't ever be offered in boxed, retail versions, only to OEMs for use in business workstations.

I checked a couple things, and for some reason I kept typing XD instead of EDB. Thanks for the correction.

EM64T and x86-64 are not the same. Although they will both run the same code most of the time. Intel's faq on the subject even states that in most cases they will be compatible. But never states they will be 100% of the time.

I did see that about the 3.4F and 3.2F. According to Intel's presenters at the last ICC event I attended, they do plan to offer EM64T enabled CPU's as boxed processors. This could have changed recently, but if they sell will sell to OEM's outside of Dell and HP/Compaq and so on, I'd be really shocked if they didn't sell them as boxed processors to the general public.

They have actually added a "J" to a couple models, such as the 560J and 570J to denote EDB functionality. This is taken from Intel's website. So the naming scheme has changed somewhat. But you are correct in that the 3.2F,3.4F, and 3.6F are listed by clock speed and not model number.

I've also edited my post to reflect the corrections.

when are they going to call it pentium 5!? will there ever be one?
my personal thinking on this is, if intel is now immetating amd, better for me to get an amd64 next!?!! right?!!!

Originally Posted by JVC

when are they going to call it pentium 5!? will there ever be one?
my personal thinking on this is, if intel is now immetating amd, better for me to get an amd64 next!?!! right?!!!

Intel's next chip will not be named Pentium at all. Pentium 5 is kind of redundant. Intel has often immitated other processor manufacturers. Brand prediction in the Pentium II was taken from the Cyrix 6x86. Does that mean Cyrix had a better processor? No. Intel is still pushing the industry in all kinds of directions. PCI-E, DDR2, low voltages in the Pentium M line.

Intel just took a couple features that their competition has and copied them. It's only good business.

The naming scheme also represents Intel's new school of thought which stresses performance over clock frequency. It's an industry-wide trend, really.

Originally Posted by Sir-Fragalot

I checked a couple things, and for some reason I kept typing XD instead of EDB. Thanks for the correction.

EM64T and x86-64 are not the same. Although they will both run the same code most of the time. Intel's faq on the subject even states that in most cases they will be compatible. But never states they will be 100% of the time.

I did see that about the 3.4F and 3.2F. According to Intel's presenters at the last ICC event I attended, they do plan to offer EM64T enabled CPU's as boxed processors. This could have changed recently, but if they sell will sell to OEM's outside of Dell and HP/Compaq and so on, I'd be really shocked if they didn't sell them as boxed processors to the general public.

They have actually added a "J" to a couple models, such as the 560J and 570J to denote EDB functionality. This is taken from Intel's website. So the naming scheme has changed somewhat. But you are correct in that the 3.2F,3.4F, and 3.6F are listed by clock speed and not model number.

I've also edited my post to reflect the corrections.

I know for sure the 6xx series Prescotts coming in February of next year will support EM64T. They will definitely be available as boxed, retail packages. These Prescotts will have 2MB L2 cache and EIST. However, I'm beginning to doubt if Intel is ever going to sell the 1MB L2 cache Prescotts with EM64T in a boxed package. But we can hope!

You're correct about the 'J' indicating EDB. What it actually indicates is that its an E0 stepping CPU. This is the new stepping that includes EDB, Enhanced Halt-State C1E, and Thermal Monitoring 2. They're reported to run cooler at idle than the older D0 stepping but the same at load. They also seem to overclock slightly higher than the D0 stepping.

Unfortunately, the only 'J' CPUs available in boxed retail right now are the 570J (3.8GHz) and the 560J (3.6GHz). I've been unable to find any of the lower clocked E0 CPUs for sale and in stock anywhere online.

Originally Posted by DanIdentity

I know for sure the 6xx series Prescotts coming in February of next year will support EM64T. They will definitely be available as boxed, retail packages. These Prescotts will have 2MB L2 cache and EIST. However, I'm beginning to doubt if Intel is ever going to sell the 1MB L2 cache Prescotts with EM64T in a boxed package. But we can hope!

You're correct about the 'J' indicating EDB. What it actually indicates is that its an E0 stepping CPU. This is the new stepping that includes EDB, Enhanced Halt-State C1E, and Thermal Monitoring 2. They're reported to run cooler at idle than the older D0 stepping but the same at load. They also seem to overclock slightly higher than the D0 stepping.

Unfortunately, the only 'J' CPUs available in boxed retail right now are the 570J (3.8GHz) and the 560J (3.6GHz). I've been unable to find any of the lower clocked E0 CPUs for sale and in stock anywhere online.

Those are the only two I've seen even on Intel's site. They just mention the 560 and 570 J's

Originally Posted by Sir-Fragalot

Q: Is EM64T compatible with x86-64 instructions?

A: EM64T is Intel's implimentation, x86-64 is AMD's. While they are not exactly the same, for all intensive purposes they are compatible. According to Intel's site they will be perfectly compatible in most cases.

There are no application instruction differences (i.e. all x86-64 *programs* will run), but there are 2 "fast task switching" instructions that intel doesn't have. The reason they are missing from EM64T is because AMD disabled the 2 instructions and removed both from the system programming guide, then later re-enabled both. For a while those 2 instructions weren't part of the x86-64 spec anymore.

It is not a problem for applications or games, just for the OS. And even that isn't much of a problem since it's easy to work around or not even used at all (using IA32-style task switching, for example).

I've had a boxed 3.4F for the past month or so.

It's an SL7L8, D0, EM64T

Pack Date: 9/7/04

Where did you get your 3.4F from?