why not 400mhz??

[9lives]

I got a newbie question.

I was browsing some of the threads and I noticed many users were using a FSB 400 MHZ CPU but why were they setting their bios to 200 mhz??

For example if I have a P4 2.0( 400 FSB), it will be better if i set it 400 mhz * 5. But why are people setting it at 200*10 ?

Thanks.

 

[Peter]

Because it IS 200 MHz for the Athlons, and 100 for the P4 CPUs, actually. They are using DDR and QDR technology, respectively, to double/quadruple the throughput of data transmissions, but the actual frequency that is being run is what I first said. It's the marketing folks who made 200 MHz DDR "FSB400" on the AMD side, and who made 100 MHz QDR "400 MHz" on the Intel end.

 

[9lives]

I am still confuse, let's put it this way :

I am going to buy a Asus P4P800 , Pentium 4 2.0A 512k 400 FSB and 2 pieces of Kingston 512MB PC-3200 400 MHZ DDR SDRAM . Do I need to manually configure the bios or let it dectect automatically? I want it to run at 400 FSB. I am not interested in OC.

Thanks.

 

[Peter]

The "FSB800" mainboard actually is 200 MHz quad-pumped, the RAM is actually 200 MHz double-pumped.

There is no 400 MHz FSB. P4 started out at 100, and now are at 200.

That 2.0A GHz Pentium-4 might very well be the old 100 MHz model. That's old stuff. Get the currently preferred version with twice as fast front side bus. Else that 200 MHz DDR RAM would be kind of wasted.

 

[9lives]

How do I know it that CPU I am going to purchase is 100 mhz or 200 mhz?

I am looking at a online price guides. But it never mentioned it was 100 mhz or 200 mhz, it only mentioned the fsb.

Thanks again.

 

[DieHardware]

I think its; A=100MHz, B=133MHz, and C=200MHz

All C's being HT enabled and all of them quad pumped (i.e.FSBx4)

 

[Peter]

That's how I remember it too. Get a "C" suffix processor if you want 200 MHz bus ("800 MHz" in marketingspeak).

 

[9lives]

I see.

Finally , all PC3200 RAM is running at a internal clock of 200 mhz?

 

[JimRaynor]

There *IS* such a thing as a 400mhz fsb P4..

They came in flavors: 400mhz, 533, and 800.

And you can't just set the multiplier to like 1 and have your fsb at 2000.

For one thing, I think Intel's processors are mulitplier locked. Another, good luck finding a chipset and ram that will do 500mhz (500mhz quad pumped = 2000). Ram tops out at about 200mhz right now, anything over that is most likely just tested at overclocked settings and branded as something higher.

 

[DieHardware]

Originally posted by: JimRaynor
There *IS* such a thing as a 400mhz fsb P4..

They came in flavors: 400mhz, 533, and 800.

And you can't just set the multiplier to like 1 and have your fsb at 2000.

For one thing, I think Intel's processors are mulitplier locked. Another, good luck finding a chipset and ram that will do 500mhz (500mhz quad pumped = 2000). Ram tops out at about 200mhz right now, anything over that is most likely just tested at overclocked settings and branded as something higher.

Did you even bother to read the previous posts? And its MHz not mhz.

 

[Peter]

Originally posted by: 9lives
I see.

Finally , all PC3200 RAM is running at a internal clock of 200 mhz?

Almost right. PC3200 RAM is indeed capable of running a maximum clock of 200 MHz, double pumped and 64 bits (eight bytes) wide to achieve a theoretical throughput of 3200 MBytes per second, yes.

But the clock is external to the DIMM, coming in from the mainboard, the RAM chips synchronizing to it That's why the stuff is called SDRAM (synchronous dynamic random access memory).

 

[Doh!]

Originally posted by: JimRaynor
There *IS* such a thing as a 400mhz fsb P4..

They came in flavors: 400mhz, 533, and 800.

And you can't just set the multiplier to like 1 and have your fsb at 2000.

For one thing, I think Intel's processors are mulitplier locked. Another, good luck finding a chipset and ram that will do 500mhz (500mhz quad pumped = 2000). Ram tops out at about 200mhz right now, anything over that is most likely just tested at overclocked settings and branded as something higher.

Sorry, but you have no clue what you're talking about.

 

[Cerb]

100MHz = 200MHz DDR FSB (Athlon) = PC1600 RAM, AKA DDR200 = 400MHz FSB P4A
133MHz = 266MHz DDR FSB (Athlon = PC2100 RAM, AKA DDR266 = 533MHz FSB P4B
166MHz = 333MHz DDR FSB (Athlon) = PC2700 RAM, AKA DDR333 (It's actually 133 1/3 and 166 2/3, if you're wondering why it doesn't go to 332...33 1/3MHz increments)
200MHz = 400MHz DDR FSB (Athlon) = PC3200 RAM, AKA DDR400 = 800MHz FSB P4C

 

[pspada]

Maybe this will help. Yes, PC3200 aka DDR400 does run at 200Mhz. But the DDR = Double Data Rate, basically a way of accessing the memory on both the rising and falling sides of the clockcycle for an effective speed of 400Mhz. The older SDR (Single Data Rate) only accessed once per clockcycle, and thus was limited in comparison. I'm not certain, but I don't think they every even made any SDR that ran faster than 133Mhz.

And that's why some mobo's like the ECS K7S5A Pro could use either. It has 4 slots, 2 SDR, 2 DDR - but you could only use one type at a time, of course. But it did not matter to the mobo, it's running at the 133Mhz, just once per clockcycle if you have SDR, or twice per clockcycle if you have DDR. Probably a way to allow people to upgrade the mobo, but keep the old SDR ram until they could afford to buy some DDR.

 

[Cerb]

Originally posted by: pspada
Maybe this will help. Yes, PC3200 aka DDR400 does run at 200Mhz. But the DDR = Double Data Rate, basically a way of accessing the memory on both the rising and falling sides of the clockcycle for an effective speed of 400Mhz. The older SDR (Single Data Rate) only accessed once per clockcycle, and thus was limited in comparison. I'm not certain, but I don't think they every even made any SDR that ran faster than 133Mhz.

PC150 and PC166. They weren't official standards, IIRC, but like PC4000, you could buy them.

And that's why some mobo's like the ECS K7S5A Pro could use either. It has 4 slots, 2 SDR, 2 DDR - but you could only use one type at a time, of course. But it did not matter to the mobo, it's running at the 133Mhz, just once per clockcycle if you have SDR, or twice per clockcycle if you have DDR. Probably a way to allow people to upgrade the mobo, but keep the old SDR ram until they could afford to buy some DDR.

Or put SDR in it when you upgrade another machine, and the K7S5A happens to have the DDR (this should be happening within the week, actually), but the PC being upgraded has the same amount pf PC133.