Async vs Sync memory timings

[stardust]

Hi, I have heard and learned about both Async (x:x) and Sync (1:1) ratios and have used both methods. I know that async is helpful to get high speed DDR like PC3500 running for 533mhz cpus. Sync is used with the newer 800mhz fsb cpus because with dual Channel DDR, both the memory and fsb bandwidth is at 6.4gbps and theres no need for async ratios.

I want to know the performance difference between async and sync timings. I remember somewhere in the back of my mind that Sync gives faster benchmarks that Async, and that sync ratios give better overclocking abilities...would anyone who knoes about this stuff brief me on the diff between Sync and Async.

thnks alot!

btw..my goal is to overclock a 533fsb to 800mhz..so u see why i need to know this

motherboard im going to use is: Asus P4P800 Deluxe

 

[pspada]

Here's and example of how it works for AMD: If you run the chip at 166fsb, your RAM should run at 333Mhz. However, you can set the memory 400Mhz (PC3200), thinking you'll get better performance if the RAM runs faster, right? But that is generally not the case, the fact that the RAM is at a different speed than the FSBs 166/333, it actually tends to slow down the system because additional wait states are induced when accessing the ram.

Now, if your lucky, an Intel dork wil explain the Intel stuff.

 

[stardust]

hahaha alrite thnks!
would async be slower to the point where a 33mhz increase actually equals less bandwidth than a 33mhz slower sync timing?

 

[pspada]

If I understand your question correctly, yes. Meantime, on the Intel side, the 533fsb is based on RAM timings that are basically 133Mhz, so it really uses PC2100. The new 800Mhz uses a fsb of 200, "quad-pumped" bla bla for the 800Mhz. So your ram better overclock to 200/400Mhz or be PC3200 to begin with. Assuming of course your chip, motherboard, video, etc can handle the overclocks as well.

 

[stardust]

yah... im going to be using dual channel PC3500 low latency...u can see my rig below...only difference would be a 533mhz P4.
eck, im jus doing this for the hell of it...i jus wanna see if i can push 200x4 on a 133x4 cpu. I've seen athlons do it..pretty amazing stuff

im gunna dig up my good ol' water cooling kit and give this a shot...i'll post results when im finished testing

 

[Duvie]

Dont forget the fact that synch with amd is usually optimal cause anything past it for memory produces more bandwidth then the cpu can handle.....

Ie 333fsb chip (166fsbx2) = 2.7gb/s (usually 2500's in sandra) while 333mhz ddr (166fsbx2) also has a peak bandwidth of 2.7gb/s.....if you bump the memory up to 400mhz ddr with a memory ratio you will memory with a peak of 3.2gb/s yet the cpu is still limited by it 2.7gb/s.....


Now for Intel systems this gets more messy...

With single channel DDR systems the memory in single channel mode is hard press to even meeet the needs of the cpu and thus in these systems 3:4 or 4:5 ratios really give benefits above 1:1 ratio alone....

NO with DCDDR systems we are aprroaching ddr matching theoretical bandwidth of the p4 cpu....

533fsb system produces 4.2-4.3gb/s of peak bandwidth which matches dual pc2100 (2.1gb/s a piece) however in most test it only seems to equate to 3.2gb/s delivered....I have seen with many in systems like this where an async memory ike a 3:4 or 4:5 once again delivers a performance increase....

I cannot attest to am 800fsb system but in most cases 1:1 ratios stop becoming an option when ocing as we are starting to reach current rams physical capabilities...

 

[Jadow]

If I overclock a P4C 2.6 to 3.25ghz (13*250) and run the ram at 4/5 ration (which is not in sinc with the FSB) will there be a problem with running the ram slower? Is there a performance loss?

 

[Duvie]

Originally posted by: Jadow
If I overclock a P4C 2.6 to 3.25ghz (13*250) and run the ram at 4/5 ration (which is not in sinc with the FSB) will there be a problem with running the ram slower? Is there a performance loss?

versus a 1:1 ratio probably so but the fact is do you have memory capable of doing 500mhz ddr at any cas timings??? probably not (there is some however!!)....Therefore look at it this way....You may have to drop you oc down to 230fsb to get it to run at 1:1 ratio but then you lose over 260mhz of raw clock speed and in my testing that is far more important then memory speed and memory bandwaidth alone.....

At 250fsb with a 5:4 ratio means you are running 400mhz ddr and likely have some room to play with in the ram either it be more aggressive timings or more fsb speed increases...

 

[ErikaeanLogic]

The main thing to be concerned with, stardust, is that some folks have had a problem overclocking a 533 cpu in the 166-199 fsb range on a P4P800 Deluxe, myself included. My 2.4B used to run at 3474MHz (193fsb) on a P4G8X at 1.6Vcore but will not run between 166-199fsb; if I boot at 200fsb it goes into Windows but is not stable (duh, I already knew that 3600MHz would be too much for this cpu). Do a search on these and the abxboards.com forums and you will see that others are having this issue, too; some of them are able to work around it with the 1006 bios, I was not. I was not able to run these fsb's on the non-Deluxe, either, but THUGSROOK has had phenomenal success with his 2.53 on a non-Deluxe. I would consider an Abit IS7 as an alternative.

HTH

 

[Dustswirl]

*popping up his head intruding*

Hi there

Can i ask a lil question? am waiting for a barton 2500 and a 3500 memory stick for my a7n8x... can't i underclock the memory a lil and overclock the fsb "ascincingly" to a point where "harmony" is reached? or should i get a slower memory?

 

[ErikaeanLogic]

Originally posted by: Dustswirl
*popping up his head intruding*

Hi there

Can i ask a lil question? am waiting for a barton 2500 and a 3500 memory stick for my a7n8x... can't i underclock the memory a lil and overclock the fsb "ascincingly" to a point where "harmony" is reached? or should i get a slower memory?

Erm, not sure what you're asking there but I'll give it a shot. Basically, with an AMD cpu you can raise/lower the default cpu multiplier so that you can raise the fsb up to the limitation of the memory spec. You'll want to run synchronously (fsb/mem) because the Athlon is not nearly as memory-bandwidth starved as the P4 and so will benefit greatly from increasing the fsb and lowering the multiplier. For example, if you have an AMD cpu you know can do 2GHz, the order of "multi x fsb" you might choose from might be 15x133, 12x166, or 10x200 (in order of increasing performance). The trick is to find the maximum stable overclock your cpu can handle (a whole other topic), find the maximum speed your memory can run with the fastest performance timings (yet another topic), and create a MHz/muliplier = fsb type of config for your system. An example of this is that if I have an Athlon XP which does 2200MHz with total stability, and memory which does 200fsb with the tightest timings, I'd choose to run the system with an 11 multiplier and 200 fsb (11 x 200 =2200, right?) for the maximum performance which the system can provide. That make sense?

HTH

 

[Dustswirl]

Perfectly (took a lil concentration though ) ! thx a lot :beer: :beer:

i hope am lucky and that this barton prooves to be a good overclocker! coz there rams are rated 434MHZ!!!

 

[Duvie]

Originally posted by: Dustswirl
Perfectly (took a lil concentration though ) ! thx a lot :beer: :beer:

i hope am lucky and that this barton prooves to be a good overclocker! coz there rams are rated 434MHZ!!!

Like what was mentioned above you can hit ram limit with no overall clock ocing just by lowering multiplier and raising fsb...

At 433mhz ddr you should look for a 217fsb....That could be a mobo limitation long before the ram...how are these mobos at consistently hitting 200+ fsb???

I would try to set the fsb at 200fsb off of the bat and lower the multiplier to keep it close to overall cpu clock and make sure the ram at 400 is fine (no compatability issues) and the boar can handle 200fsb...Then I would raise it from there on the way to 217fsb...When you hit mobo limit or ram limit then start raising the multiplier at .5 intervals (if you have them to pick)...

That is how I would do it to find a perfect balance with my sticks and oc as high as I can....

 

[Dustswirl]

Duvie <<< gr8 info!!!! Thx pal!!! :beer: got Corsair's XMS 3500C2 a A7V8X and the barton and according to Corsair's tech paper/compatibility this should work oced of course

 

[stardust]

Thnks alot erik! i have sum more questions : so the P4P800 D can't take 166-199?? and boots on 200? heh that sounds weird to me..I took my 2.66ghz to 170fsb before and it worked perfectly. I couldn't go any further because i was using bad ram and loose timings. I want to try and hit 200fsb, and I need to know whether i should use synch or async timings. I am satisfied with just DDR400 on a PC3500 as long as i can hit that 200mark because i've seen Sync DDR400 perform better than Async DDR417. My 2.66ghz is also a very good processor, one of the mVIDS...so can i have sum more tips about the memory timings i should use??

going to try to hit 200fsb with:

2.66ghz @ 1.65V-1.7V
Asus P4P800 Deluxe bios revision 7
ThermalTake aquarius water cooler
OCZ PC3500 EL Dual Channel @ 2-7-3-3 and 1.8-1.9V

PS

what are the AGP dividers on this motherboard??
and is there ANY way i could unlock the p4 so i can adjust its CPU multiplier?

THANKS ALOT PPLS!