Is it a waste?

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Guest

Guest
What's the use of the 200MHz FSB of the Duron if I use PC100/133 instead of DDR RAM.Wouldn't the speed difference go waste, since the RAM can run only at 100/133MHz?

<b>HardHardMan</b>
 

jlbigguy

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The FBS of the Duron is 100mhz, but is double pumped, transfering data 2 times per clock cycle, for an effective data transfer of 200mhz. If your motherboard supports 266mhz, then the FBS is 133mhz, double pumped.

Memory timing is asyncronous, and can run at 133mhz even if the FBS is set to 100mhz (200mhz double pumped).

It is to your advantage to use PC133 memory even if your motherboard only supports 100mhz fsb. The BIOS has the settings for memory speed.

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G

Guest

Guest
Thanks for responding.
But I am still confused about this FSB stuff. As far as I know the FSB is the same as memory bus, isn't it? Then if the duron processor accesses the memory at 200MHz FSB effectively ,100MHz double pumped.....again confused :( ,then will a PC133 capable of running only at 133MHz be able to provide the necessary speed of data transfer???
I hope u got me.


<b>HardHardMan</b>
 

Kelledin

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With PC133, a Duron or Athlon system has to run the memory bus asynchronously relative to the FSB. That means that on your Duron (with 200MHz effective FSB) paired with PC133, an effective 66MHz (33MHz DDR) of the FSB bandwidth is not used for memory. That isn't to say the leftover 66MHz isn't used for other things though, like maybe communicating with the PCI bus. So it may not be a total waste...

Kelledin

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Boondock_Saint

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Why are people saying that buying PC133 for a 100MHz bus is better? To my knowledge, all it is, is a waste of money. 133MHz RAM can only transfer at 100MHz on a 200MHz bus; the extra 33 is just being wasted. It acts nothing like a DDR type setup. That bandwith physically CANNOT BE USED. Hence buying 100MHz ram for 200 MHz buses (100x2), and 133MHz ram for 266MHz buses (133x2). Now, you can use 100MHz RAM for 266MHz buses, as you are only downgrading, putting less bandwith through, and are still under 133MHz. It is not possible though to get any benefit using 133MHz RAM in a 200MHz bus. At most you might get faster access times, but then you can get the same thing from 100MHz RAM without the added cost of a higher thoroughput. That is the only thing I am not sure of.
 
G

Guest

Guest
As far as I know Duron comes only with 200MHz FSB.So I should choose between DDR 1600 or PC133 or PC100?? As boondock sez a 133 only runs at 100megs.So there's no use of 133 except for faster access time isn't it.?

So after all that...what should I go for?


<b>HardHardMan</b>
 

DSutcliffe

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Kelledin already mentioned it:

The KX133, KT133 and KT133a have the capability of running the memory clock asynchronously from the CPU's FSB.

Since the CPU is basically almost always starved for data, the faster you get it that data the faster your computer has a chance of being. This is also why the faster the memory the better.

So no it is not a waste to have a faster memory bus than processor FSB with the above mentioned chipsets.

If you don't believe me, clock the memory to 100mhz and run some benchmarks. Or better yet find one of the many documents written on various hardware websites about this very issue.

Check out my rig:
<A HREF="http://www.anandtech.com/mysystemrig.html?id=3737" target="_new">http://www.anandtech.com/mysystemrig.html?id=3737</A>
 
G

Guest

Guest
I dont think you quite understand.
There is fsb speed between CPU and northbridge, and there is memory speed between memory and northbridge.

Now, a Duron uses a fsb of 100 Mhz, but because of the DDR nature of the bus, it performs like a 200 Mhz bus. most chipsets support asynchronous memory access, meaning the memory bus can work at 133 Mhz, while the fsb is only 100 (x2). It seems obvious that even a 133 Mhz memory bus cannot saturate a 100/200 Mhz-ish fsb, and will perform better then a 100 Mhz memory bus. THe remaining band with of the fsb (200-133=66 Mhz) is used for PCI and other stuff.

Also, you mention price.. actually, PC133 is cheaper than PC100 where I live. You would have to be nuts to buy PC100 now. PC100 or PC133 relates to the maximum rated operating speed of the module. Its true of course that a P133 DIMM will not work faster on a 100 Mhz bus (disregarding CAS latency)

Unfortunately, real world performance is somewhat different. It appears most chipsets perform much better when running fsb and memory busses in synch. Performance increases by about 10%, annihilating the advantage of the higher memory bus. IN other words, a Duron with a 100/200 fsb running @800 Mhz with a 133 Mhz memory bus, will be just about as fast as one with a 100 Mhz memory bus. However, running that same Duron @800 with a 133/266 Mhz fsb (6.5 multiplier) and 133 Mhz memory bus will perform about 10% better..somwhere between a Duron 850 and 900. Something to keep in mind when overclocking. Here is an extract from aces:
<i>
The biggest benefit of the VIAKT133A compared to the VIAKT133 is the ability to run the FSB in sync with the memory. <snip> Our measurements show that the running the FSB and memory in sync provides a 10% boost of performance in memory intensive games. Our loyal readers might remember that we explained a few months ago why running with a synchronous FSB and DRAM reduces access latency significantly. </i>

Read more about this here:
<A HREF="http://www.aceshardware.com/Spades/read.php?article_id=5000174" target="_new">http://www.aceshardware.com/Spades/read.php?article_id=5000174</A>

and here:
<A HREF="http://www.aceshardware.com/Spades/read.php?article_id=25000184" target="_new">http://www.aceshardware.com/Spades/read.php?article_id=25000184</A>

---- Owner of the only Dell computer with an AMD chip
 

Crashman

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First point, PC133 is CHEAPER than PC100 in high-volume countries. This is because it is over produced.
Now, most newer VIA chipsets support running the CPU and memory ASYCHRONOUSLY! That means that the Processor bus and the Memory bus each get their own independant clock speed. So with these chipsets, you can run your CPU bus at 100 and your Memory bus at 133!

Video killed my Radio Card!
 
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Guest

Guest
Thanx a lot bbaeyens, for clearing my concepts about FSB and Memory bus.
So, as u are saying, without overclocking the FSB I would be getting performance similar to PC100 for PC133.
So my question remains the same,what's the performance gain that I get on using PC133 over PC100. Also I would like to know about DDR and its performance gain over the rest of the lot.

<b>HardHardMan</b>
 

jlbigguy

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My system has the VIA KT133 chipset. With the memory set at HSTCLK + PCI(133mhz) vs HSTCLK (100mhz) I see about a 20% increase in benchmarks at HSTCLK + PCI(133mhz).

At either setting, the FSB is still 100mhz, but at HSTCLK + PCI, the memory is running at 133mhz.

It is to your advantage to use PC133 memory even if your FSB is limited to 100mhz.

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Matisaro

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LoL yeah that wasted 50 cents (the difference between pc100 and 133) is really killing the whole price/performance of his setup.

~Matisaro~
"Friends don't let friends buy Pentiums"
~Tbird1.3@1.55~
 
G

Guest

Guest
Thanx a lot everybody!!
So I have decided to get PC133 for my new system.At last!! :)
But then what about the AMD supported DDR memory. Can anyone tell me what's the big thing about DDR over PC133.Should I go for a mobo supporting both or just ignore this DDR stuff?

<b>HardHardMan</b>
 

AMD_Man

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DDR is not bad. In fact, it has noticable performance gains in some apps. However, only the AMD 760 chipset provides these gains. When you said a board that supports both, like the Asus A7A266, then I would say that it's not worth it because the gains in performance are not worth the losses. In some instances, the Asus A7A266 is worse in performance with DDR RAM than an Asus A7A133 with PC133. I personally would recommend the Abit KT7A-RAID, due to it's RAID functionality and 6 PCI slots.
 

Matisaro

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Kt7a raid has 5 pci slots and 1 isa slot, the KG7 raid has 6 pci slots and has amd760 northbridge. I assume this is what you meant.

~Matisaro~
"Friends don't let friends buy Pentiums"
~Tbird1.3@1.55~