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AMD AM2: More than just a Memory Change
AMD AM2: More than just a Memory Change
Date: February 6th, 2006
Topic: CPU & Chipset
Manufacturer: AMD
Author: Wesley Fink
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AMD AM2: More than just a Memory Change

The new AMD technology refresh, now called AM2, will bring DDR2 memory to the Athlon64 on-processor memory controller. Many in the industry have speculated about the impact of this low latency memory controller on DDR2 performance, which to this point has suffered under the impact of the higher latency Intel Netburst architecture. We are looking forward to the opportunity to take a closer look at DDR2 performance on AM2 - which is everyone's big question.

There will be more than just new memory with AM2, however. We now have details on the new Socket 940 for AM2. It has been widely reported that the new Socket 940 will not be compatible with the existing Socket 940 used for Opteron and early Athlon 64.

Photos of the back of the new AM2 processor show how very close the new design is to the current Socket 940.

AM2 Processor


Current Socket 940 (Reversed)

By flipping the current 940 socket photo and comparing pin-outs to the back of the AM2, you can clearly see the top 2 "lands", areas without pins, are identical in the current Socket 940 and the AM2 Socket 940. However, the bottom two lands are in different locations. The bottom right land is the same 2 pins up, but 7pins form the edge instead of the 5 in the current 940 design. The left land is also in the same row position as the current 940, but it is 6 pins from the left edge instead of 8 as in the current 940 design.

The AM2 940 and current Opteron 940 are so close in design; you have to conclude that AMD could have used the same socket design. But there are numerous electrical differences and different memory is required. AMD apparently used a revised Socket 940 to prevent any possibility that AM2 chips might get accidentally mounted in current Socket 940 motherboards. That is probably a very wise decision.

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50 Comments - Last by WhoBeDaPlaya, 1381 days ago
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RE: Little Sense by mesyn191, 1383 days ago
No, they'd have to put 2 memory controllers on there in order to be able to use DDR and DRR2 with the same chip, they'd probably also have to add several hundred more pins to the package to greatly increasing costs... You're also forgetting increased motherboard costs as you'd need 2 different sets of RAM slots on the motherboard which would be difficult to route properly that close to the CPU, you'd probably need 8 layers or more just like on a server motherboard and those cost a bundle.

Its a silly, pointless idea anywhich way you look at it as even if you could make it cost effective you'd only be able to have a 8GB RAM drive (assuming 4 DDR RAM slots) max, which is much to small to be worth anything, not to mention the cost of 2GB DDR DIMMs which even at PC2100 speeds cost $156 a piece. What a waste of money...

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RE: Little Sense by mesyn191, 1383 days ago
I doubt that'll ever happen as outside of the server market socket 940 chips are unusual, socket AM2 is for consumers... Also the raised portions on the socket itself should prevent the chip from even laying flat in the first place, there isn't any way anyone with half a brain to screw it up as they'd have to use a hammer to flatten it out and even an idiot would know you don't use a hammer to install a CPU LOL.

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RE: Little Sense by DigitalFreak, 1383 days ago
I think Intel sticks to the same socket for as long as AMD does, but they change their VRM requirements a lot.

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RE: Little Sense by breethon, 1383 days ago
I just sunk over $700 into a rig with a new Venice core 939 cpu, right before the 940 revolution started(like a month)....oh well. The main reason I switched from Intel (had Intel since my Pentium 150 classic)was the fact that every upgrade i needed to buy a new stinking motherboard. I was totally impressed with the way that AMD stuck to their socket design for soooooo long......DOH!

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RE: Little Sense by WhoBeDaPlaya, 1381 days ago
Tell me about it. Socket A is still kinda alive for crying out loud.
Long live Socket 754! :P

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by hans007, 1383 days ago
i think the whole northbridge so we can use different ram types idea is why intel sticks witha northbridge.

i mean, i do find it rather limiting when i work with an AMD based system, that say i HAVE to use registered dimms on opterons, have to use only normal dimms on normal Athlon 64s etc, when on an intel setup you can just buy the motherboard that fits your memory (and motherboards are cheaper than memory in most cases)

Intel may never go to an onboard controller and may just try to reduce latency on their current ones (nvidia has proven they can reduce it more than intel).

The fact that the socket is so similar and is also 940 pins no doubt will lead to people putting the wrong chip in the socket, ordering the wrong type etc.

I dont understand why they didnt just add like 10 random pins. say make it socket 945. at least people would not order the wrong item, etc or even come close to confusing it. And why the hsf change? granted its mounted with 4 screws instead of 2 (i.e. like intels) but what is the point. they probably only have that for heavier heatsinks (perhaps they actually need heavier hsfs who knows).

Anyhow, I doubt this refresh is going to make any difference performance wise, if anything it reduces computer manufacturing costs, since DDR2 is already cheaper than DDR and the gap will continue to widen.

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AM2 by PrinceGaz, 1383 days ago
I suppose they could have added an extra pin and called it Socket 941, but there shouldn't be any confusion anyway as it is called "Socket AM2", not "New Socket 940". The only people that could spread potential confusion are those that insist on referring to it as a new socket 940, rather than correctly calling it socket AM2.

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Makes little sense.... by mesyn191, 1383 days ago
i mean, i do find it rather limiting when i work with an AMD based system, that say i HAVE to use registered dimms on opterons, have to use only normal dimms on normal Athlon 64s etc, when on an intel setup you can just buy the motherboard that fits your memory (and motherboards are cheaper than memory in most cases)

Opterons are for server use only, and in a server registered DIMMs are pretty much a standard requirement so I have no idea in the world why you would complain about that... Or why you'd complain about not being able to use em' on a regular A64, they're slower and more expensive than regular DDR DIMMs and consumer grade hardware (like a A64) doesn't need the added RAS support that registered DIMMs can provide.

Intel may never go to an onboard controller and may just try to reduce latency on their current ones (nvidia has proven they can reduce it more than intel).

An ODMC will always be significantly faster than a northbridge, ecspecially for DDR2 which has significantly higher latency than DDR.

I dont understand why they didnt just add like 10 random pins. say make it socket 945. at least people would not order the wrong item, etc or even come close to confusing it. And why the hsf change? granted its mounted with 4 screws instead of 2 (i.e. like intels) but what is the point. they probably only have that for heavier heatsinks (perhaps they actually need heavier hsfs who knows).

More pins cost more money, the amount they already have on the package is amazing for a mass produced product, probably eats up a large portion of thier per chip profits. There is a reason why Intel went with a pinless package you know, and it wasn't just because of bus singaling issues... 4 hole HSF mounting distributes the pressure more evenly over the motherboard surface, prevents the PCB from flexing when mounting a HSF.

Anyhow, I doubt this refresh is going to make any difference performance wise, if anything it reduces computer manufacturing costs, since DDR2 is already cheaper than DDR and the gap will continue to widen.

If you're expecting 20%+ performance gains then yea, you WILL be dissappointed, but 10% or so is not out of question with a new ODMC + DDR2.


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Well, shite... by DigitalFreak, 1383 days ago
I guess I won't be moving my XP-120 cooler over from my P4 system when I upgrade. Thanks AMD!

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RE: Well, shite... by PrinceGaz, 1383 days ago
You'll be fine, the existing XP-90[C] and XP-120 come with an adapter for S478, and another for S754/939/940. To use the heatsinks with LGA775, you have to buy a LGA775 adapter that ThermalRight sell seperately for US$5. I would wager that Thermalright will simply produce an AM2 adapter for the heatsinks in due course, so for around US$5 you'll be able to use your XP-120 with an AM2 socket.

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