memory questions

[alchemist]

hey, after sorting out the raid stuff yesterday, i had some questions about memory or ram too =P

well back 3 years ago, after reading overcloaking guides and stuff

from my understanding, if u had alike a pentium 4 and althon 64, you probalby running at 200 mhz stock right. Which in turns to be using pc3200, 400 mhz ram. I was somehow taught that 200 x 2 = memory speed, correct me if i was wrong, but i didn't know why it was suppose to be like that.
and 200 mhz uses, 6:2:1 divider back in the days when agp still exist,
200/6 = 33 mhz
33 x 2 = 66 mhz agp
33 x 1 = 33 mhz pci

although i do not know what mhz is pci express goes in, but i guess the logic is what i think to be like that. And most motherboard can lock both agp and pci slot.

in memory, as your freqency increases, your memory speed also increases.
so running at fsb of 250, you run the memory at 500 mhz, and 300fsb of u run at 600 mhz. I think there is ways to divide the ratio so the memory doesn't need to go up as much when fsb is increased, but can't remember.

The problem I have is that DDR 2 is running at like 800 to 1000 mhz, isn't there no way to run at that speed ? Most people i know that buys high mhz ddr1 memory before and say that they have a like a 500 mhz memory, but they are running at stock fsb freqency, which usually make me laugh.

In my understanding is that if you run at stock fsb in athlon 64, u run at 200 fsb and the memory will always be 400 mhz, a pc 3200 ? Wouldn't the tight timings in ddr 1 surprass DDR2 since not everyone overcloaks ? Why would the new x2 cores support ddr2. I've known that ddr2 has higher bandwith, but i do not know how it comes to play in terms of performance and stuff. Is there ways to make your memory run at 800 mhz at 200 fsb or something ? Or am I missing something. Hope you and I understand what I'm saying =(

[werty316]

DDR = double data rate meaning the memory bus speed is double pumped.

I think PCI-E runs at 100Mhz and is not affect by overclocking a CPU and/or memory.

Tighter timings on a DDR1 computer won't matter when DDR2 has pure speed even if the timings on DDR2 are much more loose.

AMD new socket AM2 supports DDR2.

DDR2-1000 and DDR2-800 is the rated speed the memory.

[alchemist]

but the problem i have in my logic is that
if your fsb is 200, your memory speed will always be running at 400 mhz
even buying a ddr 2 memory like 800 mhz, you would undercloak it to 400 mhz no matter what speed u buy. I know ddr 2 would have some advantage in artitecture, but at stock fsb, you would be fighting a ddr1 with a tight timing of 2-2-2-6 vs a ddr2 with 2.5-3-3-8 or higher, how would ddr 2 benefit over a ddr 1 in this case. Why would u buy a ddr 2 in this case if ur not even doing any overcloaking.

Lets even say u overcloaking, to 250 fsb, you would only need like 500 mhz ram, why would u need a 1000 mhz ram in this case ? why would higher mhz ram be any better? i'm loss =P

what i'm saying is that could u run a memory at 800 mhz on 200 fsb ? and how would it be done ? 200 x 4 ?

[werty316]

You have to use DDR2 eventually as both AMD and Intel switched over to DDR2 and will not be making new CPUs that use DDR1.

Higher MHz means more speed despite have higher (loose) timings.

[alchemist]

but still the point would be that at 200 fsb, your ram will always be running at 400 mhz no matter what ram you are running at.

but ur telling me that the higher the mhz the faster it would be.
but what if the ram is under cloaked at 400 mhz,
the difference between a ddr 1 and a ddr 2 at 400 mhz would only be the timings isn't it ?

unless your cpu/mb/ram can run at 400 fsb, your ram would never hit the optimized speed of 800 mhz that the ram is designed for.

or am i missing something ?

[werty316]

Yeah if FSB is runnnig at 200MHz the RAM will be runnning at 400MHz because DDR doubles the data transmitted.

A stick overclocked to 250MHz (500MHz effective) is faster than 200MHz (400MHz effective) because it has a faster clock speed.

Ever since the days of the AthlonXP you don't need a 1:1 overclock with an A64 computer as long as the memory is at or above 200MHz (400MHz effective). Running memory lower than it rated speed will decrease performance.

Difference between DDR1 and DDR2 at 400MHz is the timings. Because of this DDR2 at 400MHz is slower because of the looser timings.

Yes a motherboard needs to be compatible a memory specified speed rating. I f a motherboard only supports PC2-5400 (667MHz) and you want to use PC2-6400 (DDR2-800MHz) the memory will run at PC2-5400 (667MHz) unless you overclock.

[ToXic_WaSTe]

But that is where people raise their FSB so they also can overclock their ram.

Does the FSB get divivded by 4 when in dual core then? if they dont support shared FSB?

btw, pc-6400 divided by 8 = (800Mhz) pc-5400 divided by 8 = (667Mhz) see the picture? Just i case you didnt know...

[GIBSON]

Thing is that intel processors use quad pumped memory buses. This explains why you'll get a 800mhz memory speed with a 200mhz fsb. Hope that clears things up a bit.

[Das Capitolin]

But that is where people raise their FSB so they also can overclock their ram.

Does the FSB get divivded by 4 when in dual core then? if they dont support shared FSB?

btw, pc-6400 divided by 8 = (800Mhz) pc-5400 divided by 8 = (667Mhz) see the picture? Just i case you didnt know...


The FSB on an Intel CPU motherboard controls the RAM and CPU clock speeds. An 800MHz FSB system runs the CPU at 200x4 (800) and the RAM 200x2 (400). The RAM and CPU have different buses, and therefore different FSB multipliers.

[ToXic_WaSTe]

Thing is that intel processors use quad pumped memory buses. This explains why you'll get a 800mhz memory speed with a 200mhz fsb. Hope that clears things up a bit.

More or less clears thing up, but dont the 2 cores use a shared FSB??

[werty316]

Of course they share the bus since there are two cores on one chip. Why ask a question twice in two posts?

[ToXic_WaSTe]

Of course they share the bus since there are two cores on one chip. Why ask a question twice in two posts?

Just dont see the reason for divided by 4 in a 2 core chip if they share the FSB, and you are getting very antsy, maybe its because it because im high on posts, but dont worry im going on vacation in a week or so... so wont post more then you..

I'm no geuniess when it comes to chip architecture, but that doesnt require you to question my motives... LOL!

[werty316]

I don't know why the FSB is quad-pumped; its just the way its design to improve FSB performance. Read your own posts and you'll why I am "antsy".

[GIBSON]

Just dont see the reason for divided by 4 in a 2 core chip if they share the FSB, and you are getting very antsy, maybe its because it because im high on posts, but dont worry im going on vacation in a week or so... so wont post more then you..

I'm no geuniess when it comes to chip architecture, but that doesnt require you to question my motives... LOL!
This has nothing to do with the amount of cores. Actually, the motherboards which support dualcore intel cpu's all have a higher fsb than 800 (as far as i know)
It's just a matter of faster is better, if the fsb isn't high enough then the cpu gets starved for data which leaves it crippled. That's why intel ups the fsb now and then.

[Kougar]

Hark back to the Pentium 2 and Pentium 3 days... the FSB was 100FSB or 133FSB, and that was it. Compare it to a highway... Intel found it was easier to add 3 more lanes beside the one already there (for a total of 4) instead of increasing the speed limit of the 1 lane highway itself. The first Pentium 4s were 100FSB quad-pumped to 400FSB, before Intel then began raising the speed limits. 133mhz became 533mhz, 200FSB became 800mhz, and now 266mhz will be the 1066mhz FSB of the Core 2 Duo.

At stock my own P4 was a 200FSB, 800mhz QDR. Right now it is 245FSB*4=980mhz front side bus, which gives me a 3.43ghz clock speed off a fixed 14 CPU multiplier. The DDR400 RAM is running on a 5:4 ratio, so... 4x245(FSB)=980 and 5x196(DDR392)=980. So the memory is operating at an effective DDR392 due to the 5:4 ratio.

[alchemist]

ok.. after reading through the post. so i'm getting that intel has a quad pump on the memory, so u can run ddr 800 at stock 200 fsb. so thats a pc 6400 that can u run with a stock 200 fsb? am i getting this right?

and new dual core is running at 266 fsb ?

i think i'm getting it wrong still, shrugs

[werty316]

Yeah, I think you got it now.

[alchemist]

well does the quad pump does it automatically once i put the memory in and a
lets say i have a p4 at 200 fsb, quad pump makes it at 800 mhz ram speed.
which i need to use a pc 6400right ?...

what if i only had a pc 5300, 667 mhz ram
so than i would be running at 166 fsb to run it at 1:1 ratio
so i would need to use a 5/6 divider, 200 x 5/6 = 166 x4= 667 ?

i think i'm getting there... and the new dual core is at 266 fsb quad pump it u have 1064, thats how people utliize the pc 8500 i guess ?

but is it a big difference using 1:1 ratio or not on a ddr2
i've seen somewhere that on pentium 4, timings aren't as important is it ?

does the pentium theory all applies to amd as well ? or is it different ?

[Kougar]

If you are trying to find the memory speed that you need to run a 1:1 DRAM:CPU ratio, then take the full FSB speed and divide by 4. This number should then be doubled, and you will arrive at the DDR's speed.

For example, my system at stock uses a 800mhz FSB. 800/4=200mhz. So 200mhz*2 is 400, or rather DDR400 speed memory is what you need to run at a 1:1 ratio :)

Example 2: For a Core 2 Duo system, you will have a 1066mhz FSB. So 1066FSB/4=266mhz. So 266mhz*2=533mhz, or in this case DDR2-533mhz RAM is what you would use to attain a 1:1 ratio.

To answer your question with DDR2-667 RAM: 667/2=333mhz. So you would need to be running the FSB on your system at 333mhz to use the best performing 1:1 ratio. At a 333mhz FSB, you would have a QDR of 1333mhz which pretty much any Core 2 Duo processor will be able to reach easily ;)

Even though you lose the 1:1 ratio going from DDR2-533mhz to DDR2-667mhz, you still get better performance. Overclocking the FSB to the right number to let you change back to the 1:1 ratio will boost performance figures decently, if past results hold true.

Yes timings are not really that important. They will give you better performance, but the difference seems to be insignificant and not worth the price premium in my opinion.

Another thing to note is that the motherboard/CPU only present you with specific dividers to use depending on what you plug into the motherboard. The only dividers I've seen used for DDR2 are these: [4:3, 1:1, 4:5, 2:3, and 1:2]. Older DDR has used 5:4 and 3:2 ratios, besides a few of the others... Assuming you use a Core 2 Duo, these ratios in the brackets would be for DDR2-400 all the way to DDR2-1066mhz, respectively and in that ascending order.

If by pentium theory you mean the deal about timings, then definitely no. AMD systems can take some very sizeable performance hits from higher latency.