Official socket M2 confusion thread

[JAG87]

Since I am planning to build a system in june, I am waiting for M2 processors to come out. Now, my question is:

roadmaps indicate that clock speeds are going to be from 2.0 (3800+) to 2.8 (FX-62), but they also indicate that the HTT will be 333 mhz, compared to the 200 we have now. So how exactly is AMD going to clock this processors? Am I stupid or are there some major contraddictions in their roadmaps? Do you guys think that the HTT will actually be 333, and we will have 2.0 ghz, 2.33, 2.5, 2.66, and 3.0 ghz, or do you think that we will have 200, and 2.0, 2.2, 2.4, 2.6, 2.8?

post your opinions, and some links so we can get this straight!



PS. I dont know what ram to look at because of this. everything is nicely planned out, except for the ram. Its either going to be 667, or 800 depending on the HTT.

 

[Furen]

HTT will be 200MHz, not 333MHz. People (myself included) believed that HTT would be 333 because of AMD's official support for DDR2 667 (which has a 333MHz external clock), but it is not necessary to have the HTT "in sync" with the expected memory clock, as you can see from AMD's support for DDR266, 333, 433 and 466...

 

[JMWarren]

So they'll be using a ram divider greater than 1:1.....a multiplier i guess...?

 

[JAG87]

well if you run DRR2 800 it should be 1:1 because its really 200x4.

thats why, I really wanna buy DDR 800, but if then it turns out to be 333, imgona be pissed. and If I buy DDR 667 (1:2 with 333HTT) and then it turns out to be 200, im gonna be even more pissed.

 

[RichUK]

Originally posted by: JAG87
well if you run DRR2 800 it should be 1:1 because its really 200x4.

huh?! 1:1 with what?

thats why, I really wanna buy DDR 800, but if then it turns out to be 333, imgona be pissed. and If I buy DDR 667 (1:2 with 333HTT) and then it turns out to be 200, im gonna be even more pissed.

How would a 333Mhz memory bus be a disappointment? Thats 133Mhz faster than current stock memory speeds on s939.

 

[Furen]

Originally posted by: JAG87
well if you run DRR2 800 it should be 1:1 because its really 200x4.

thats why, I really wanna buy DDR 800, but if then it turns out to be 333, imgona be pissed. and If I buy DDR 667 (1:2 with 333HTT) and then it turns out to be 200, im gonna be even more pissed.

Once again, theres is no 1:1 on AMD K8 platforms. The ratio is usually the memory controller : DRAM ratio (people compare it to the FSB because the memory controller runs at the FSB clock since it's on the northbridge), which ends up being 10:1 on a 2GHz part. 1:1 would require memory that runs at a 2GHz external clock.

 

[JAG87]

man u misunderstand Rich

DDR2 800 is 1:1 with a 200 mhz FSB. the ram is running four times slower then the memory bus speed.




and 333 HT would be a disappointment if I bought DDR 800 ram, because I would have to use some gay divider. BUt if i bought 667, it would be fine. I never said I dont want 333 cause its bad. lol

 

[RichUK]

Originally posted by: JAG87
man u misunderstand Rich

DDR2 800 is 1:1 with a 200 mhz FSB. the ram is running four times slower then the memory bus speed.

Not really because the I/O buffers on the DIMM's which actually communicate with the memory bus itself (external clock) on DDR2 800 DIMM's, actually operate at 400Mhz if ran at a 1:1 DRAM ratio.

Your getting confused because the internal IC's actually run at 200Mhz, and are quad pumped on each prefetch equalling an equivalent to 800Mhz, hence why the I/O buffer can operate and fully supply bandwidth at 800mhz.

EDIT: Corrected

The I/O buffer run at 400Mhz, but can effectively supply 400Mhz worth of data on the up curve and down curve of the sine wave. Which actually effectively equates 800Mhz due to DDR technology.

 

[Brunnis]

I'm confused here. Basically, what you guys are saying is this:

If I have an A64, run the HTT on stock 200MHz and run my memory on a 5/4 divider, I'll get 8GB/s theoretical memory bandwidth, without even touching the bus speed?

I'm going to try this immediately.

 

[Furen]

Not quite, the IO runs at 400MHz at double data rate. Because of this, the the ratio would be 1:2 "HTT : DRAM" (though having an HTT to DRAM ratio is not the correct way to look at it, it's supposed to be a CPU clock : DRAM ratio).

 

[RichUK]

Originally posted by: Furen
Not quite, the IO runs at 400MHz at double data rate. Because of this, the the ratio would be 1:2 "HTT : DRAM" (though having an HTT to DRAM ratio is not the correct way to look at it, it's supposed to be a CPU clock : DRAM ratio).

whoops that?s right, 400Mhz on DDR that?s what i meant.

The I/O buffer run at 400Mhz, but can effectively supply 400Mhz worth of data on the up curve and down curve of the sign wave. Which actually effectively equates to 800Mhz due to the DDR technology.

 

[JAG87]

so am I wrong when thinking that with a 200 htt, the best ram to use is 800?
and with 333 HT, 667 would do great right?


continuation: I found sources saying that HTT will be 200 like 939 processors, so Im guessing PC6400 it is ...

 

[Furen]

You are wrong to say that the best ram to use for 200HTT is DDR2 800 and that at 333HTT it would be DDR2 667 because HTT makes no difference at all. I'm sure one of these two types of ram will be better (this depends on AMD's memory controller, but I'd guess low-latency DDR2 667 but I could be wrong) and this will be the best regardless of whether or not you use an HTT of 200MHz or 333MHz.

 

[JAG87]

you think 667 DDR2 might do better then 800 mhz (assuming 667 has tighter timings)? I am looking at crucial ballistix, the 667 has 3-3-3-12 while the 800 has 4-4-4-12, which do you think will yeild best performance?

for some reason im inclined to go 800, but give reasons not to...

 

[Furen]

I'm guessing DDR2 667 with tight timings will do better for AMD because that bandwidth should be more than enough to feed more cores, and we've seen again and again that AMD chips respond well to low latency. This is, of course, just speculation since AMD's DDR2 memory controller is a big unknown...

Here's one thing I want to add, though: I'm sure DDR2 800 will be able to do DDR2 667 with slightly tighter timings and low latency 667 stuff may be able to hit DDR2 800, so this whole conversation may be moot as long as you're willing to tweak your system manually. Personally, I'd wait for the chips to hit the market before deciding on a course of action.

 

[DrMrLordX]

Who knows? The real trick will be trying to get AM2 to outperform s939 consistantly, and that may come down to latency.

DDR2-677 at . . . 3-3-3-8 should be able to match or beat DDR400 2-2-2-5 latency-wise, no? How many DDR2 DIMMs can do that?

 

[Furen]

No. DDR2 667 at 3-3-3 is quite a bit slower than DDR 400 at 2-2-2... it's about the same speed as DDR400 at 4-4-4. Remember that though the IO in DDR2 667 runs at 333MHz, the memory chips only run at 166MHz. If you divide a second by that you'll get the time per clock. Multiply this by the latencies and you get the latencies in time.

 

[DrMrLordX]

Oh, damn. Thanks for the clarification.

That makes it rather difficult for AMD to get reduced latencies from DDR2 . . .

 

[biostud]

AFIAK the HTT isn't going to be changed until HyperTransport 2.0, so it's still going to run 5 x 200Mhz.