133MHz vs 100MHz on 200MHz FSB

HandOfDragon

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Hi everyone,

I'm curious about the basic of RAM and FSB. It's been long time since I last touch any components in my baby. My question is the new MoBo I bought have 200MHz FSB (MK33 AOpen, micro-ATX since I want to use my old IBM case). I have both 133MHz and 100MHz SDRAM on my MoBo now (100MHz is the old one). How the FSB relate to RAM clock cycle. In this case, if I change to be 133MHz RAM (all of them), will I get higher data transfer rate? or anyone would be so kind to explain what is FSB work related to RAM clock cycle =)

Thanks.
 
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Guest

Guest
Your 200MHZ FSB is really 100MHZ FSB , the AMD processor you pick will process on the rising and falling edges of the clock Effectively given you 200MHZ -> DDR. Your memory will run at 100MHZ, putting in PC133 memory won't make you system faster because the memory will still run at 100MHZ regardless. To see an increase in memory performance you will need to bump up your FSB. The advantage to having PC133 in your system would be to help in overclocking FSB, but with the KT133 the FSB can't be OC that much so PC100 would probably be fine.

Some boards recognize pc100/pc133 and will adjust the memory bus speed accordingly.

Your KM33 is the older KT133 chipset. If you had the newer KT133A or KT133E you would get 133+MHZ (266+ DDR) FSB. With the KT133 you'll top out at around 115MHZ.



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Arbee

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One thing is the bus frequency (FSB), other is memory frequency. On a KT133 the bus speed is (default) 100MHz DDR, and it is quite hard to overclock.
But the memory can be run at FSB+PCI - meaning 133MHz (at default), thus the system benefits from having a faster memory. PC133 can run at 133MHz with the KT133.

Arbee
 
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Guest

Guest
"But the memory can be run at FSB+PCI "

I don't understand that? PCI clock is generated By dividing the FSB. 100MHZ FSB divided by 3 to get 33MHZ and 133MHZ divided by 4 to 33MHZ. That's why when you OC the FSB it causes the PCI bus speed to exceed 33MHz and possibly cause your PCI devices trouble.

Some boards run the memory/cpu speed asynchronously - 133MHZ for the CPU and 100MHZ for memory if you have PC100, but I thought this was limited to the MoBos that supported a 133MHZ default bus for CPUs like Intel's EB CPUs (chipset?) and the newer AMD 266MHZ CPUs (KT133A chipsets). I don't think that the MoBO he has will run the memory asynchronously @ 133MHZ if he has PC133....

The KT133 isn't a good FSB overclocker, that's why I doubt the memory will default to 133 if he has PC133 in it...


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HandOfDragon

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I tried put in 133MHz RAM I have and the MoBo detect and run at 133MHz FSB. That's the first time I installed this MoBo with only 1 stick of memory (128MB). After that, I installed 2 more modules to get 320MB but the FSB reduce to 100MHz since the lowest FSB of all ram is 100MHz.

So, can someone confirm if I will benefit from using 133MHz FSB so that I will buy 2 sticks to replace my current 100MHz memory sticks. Thanks.
 

Ncogneto

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This may make more sense. Think of the memory bus running at a divider of 4/3 ( the same as pci+fsb).

<font color=red>Some boards run the memory/cpu speed asynchronously - 133MHZ for the CPU and 100MHZ for memory if you have PC100, but I thought this was limited to the MoBos that supported a 133MHZ default bus for CPUs like Intel's EB CPUs (chipset?) and the newer AMD 266MHZ CPUs (KT133A chipsets). I don't think that the MoBO he has will run the memory asynchronously @ 133MHZ if he has PC133....</font color=red>

No it is not limited to motherboards which support a cpu fsb of 133. It is very common to see motherboards with a cpu bus of 100 mhz ( 200 mhx double pumped) supprt a memory bus of 133. This has been very common since the kx-133. All kt-133 motherboards that I am aware of will support this as well as I815 boards.

A little bit of knowledge is a dangerous thing!
 
G

Guest

Guest
So what is the final verdict with this? The original A7V has two SDRAM timings: 1/1 and 4/3. People I've talked to say that you'll gain nothing from running the memory faster, if the FSB is at 100. Is this true? Why have the option if there's no performance gain?
 
G

Guest

Guest
Thanks, it makes now -
- 4/3, running the memory bus 1/3 faster than the cpu bus
- 1/1, running the memory bus at the cpu bus speed

I would just try and use the PC100, chance it might run @ 133. Probably need to benchmark it running @ 100 and then 133 to see what increase in speed you get. Might not make enough to notice a real difference.

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HandOfDragon

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Well, I take the 100MHz mem sticks off my comp and run it with 128MB 133MHz mem. I get much better sub-system speed (about 480MB/sec) compared to when I put 320MB 100MHz mem in (1-133 and 2-100) which I got about 300MB/sec).
 

lamer_gamer

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Strange! I just came here to ask almost the very same question as HandofDragon [x-files theme music plays]! An additional question from me: Aside from the possible performance increase, can I f-up my system having one stick of pc-100 in with two pc-133's?

My brain has performed an illegal operation and will be shut down<P ID="edit"><FONT SIZE=-1><EM>Edited by lamer_gamer on 06/12/01 02:07 AM.</EM></FONT></P>
 

HandOfDragon

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l_gamer,

It's depend on your MoBo but if your MoBo detect the RAM speed and adjust it automatically, it should be fine. As far as I know, there should not be any probelm but the RAM speed will be 100MHz if you put 1 stick of 100MHz with 2 sticks of 133MHz. I currently have 1-133MHz + 2-100MHz sticks.

When I take the 2-100MHz sticks off and run 3DM2k1, I got around 3250 compared to 2900 with old config on my Radeon card on W2K. You may want to keep only 133MHz ram. if you have more than 256MB left, it should be fine for almost all the game. I still keep the current setting (mix-RAM-speed) because I need to run Visual Studio daily.