AM2 <> AM3 compatibility

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venm11

2[H]4U
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We've all heard that AM3 cpus will work in AM2 boards with DDR2.

1) Why can't AM2 chips run in AM3 boards? Why would they prevent this?
2) Will AM3 boards support DDR2? or just DDR3?

Just looking for a smooth upgrade in a year or so.
 
It was my understanding that AM3 boards will use DDR3 and have the same socket as AM2. AM3 processors will have a memory controller for both DDR2 and DDR3 so you could use an AM3 processor in either an AM2 board with DDR2 or an AM3 board with DDR3.

I could be wrong, though.
 
not certain that this is true yet, but VG has it about right:

AM3 = support for both DDR2 and DDR3 in it's memory controller. socket will probably just have 935 pins or something, so that the AM3 chips will fit in AM2, but not vice versa. AM3 boards may support either DDR2 or DDR3, but not both. since AM2 backwards compatibility is there, AM3 will most likely be DDR3 only

AM2 = support for DDR2, but not DDR3. logically, you can't put it into something that requires DDR3, so no AM3 support :D
 
yeah the AM3's definitely support both ddr2 and ddr3. But do AM2's?

DDR2 and DDR3 are supposed to be pin compatible. So either JEDEC accounted for all scenarios like DDR2-in-DDR3-board and DDR3-in-DDR2-board, unless they're using slot keying to prevent certain combinations.

If DDR3 is a superset of DDR2, and the memory itself supports DDR2 settings, then perhaps in some situations a BIOS update could allow AM2 mobos to use DDR3 as DDR2, or some mix-n-match DDR2/DDR3 features.

That would be great for us if all the combinations were possible. But it may also be that AMD wants to enable us to buy a new chip for our old hardware, not allow us to buy new hardware for our "old" AMD chip.
 
venm11 said:
yeah the AM3's definitely support both ddr2 and ddr3. But do AM2's?

DDR2 and DDR3 are supposed to be pin compatible. So either JEDEC accounted for all scenarios like DDR2-in-DDR3-board and DDR3-in-DDR2-board, unless they're using slot keying to prevent certain combinations.

If DDR3 is a superset of DDR2, and the memory itself supports DDR2 settings, then perhaps in some situations a BIOS update could allow AM2 mobos to use DDR3 as DDR2, or DDR2 plus specific DDR3 settings/features.

That would be great for us if all the combinations were possible. But it may also be that AMD wants to enable us to buy a new chip for our old hardware, not allow us to buy new hardware for our "old" AMD chip.
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no.
 
DDR2 and DDR3 are pin compatible.

As said:
AMD's next gen CPU's will have a memory controller that supports both DDR2 and DDR3.
Because of this, and their pin compatability, the CPU's will work in both socket AM2 and socket AM3 motherboards.

AM2 motherboards will only ever support DDR2 ram and i presume that AM3 boards will only ever support DDR3 ram. Even if AM3 boards can support both, it will either be one or the other dependant on the motherboard.

This is a massive advantage for those with socket AM2 motherboards as it gives a very clear upgrade path:
K8 cpu + AM2 motherboard + DDR2 ram ---------> K8L or whatever cpu -----------> AM3 motherboard + DDR3 ram

this is why i am seriously considdering going lower end K8 X2 over high end Conroe. It looks like the upgrade path will be much more wallet friendly, so long as K8L is as good as it is shaping up to be. A nice native quad core for me in a years time :)
 
where does it say that ddr2 and ddr3 are pin compatible in there? i only see that am3 cpus are pin compatible with am2
 
Hmm... after googling, it seems like they aren't. I probably either speculated or read someone's speculation based on the fact that they're both 240-pin.

Although, I do recall that the article I read it in said that the AM2 chip would not be insertable into the AM3 socket. Hmm... I guess that's moot, isn't it?

Oh Well. :(
 
yeah, the whole situation is weird. i know there were people pushing really hard to make ddr2 and ddr3 pin compatible, but when i saw a picture of a ddr3 stick like a month ago, the notch was way off to the side, while ddr2 has it pretty close to the middle

*shrug*

it would have been nice though :D
 
Don't worry. DDR2 will be faster then DDR3 for awile. The timmings for DDR3 are insane. Like 8-8-8-10 for DDR3 1200mhz. Compared to 1000mhz DDR2 at 3-3-3-10. DDR2 like I said will be much faster for awile.
 
Serge84 said:
Don't worry. DDR2 will be faster then DDR3 for awile. The timmings for DDR3 are insane. Like 8-8-8-10 for DDR3 1200mhz. Compared to 1000mhz DDR2 at 3-3-3-10. DDR2 like I said will be much faster for awile.
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ddr2 at 500mhz, 3-3-3 is definitly one of those "only see it once every 10,000 sticks" kind of things. around 350-400mhz at 3-3-3 is good for high-end ddr2
 
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