Understanding the FSB

[hmg57]

Please tell me if I'm wrong. Theses affirmations only apply to AMD motherboards. The FSB is the CPU's own frequency. It is not the same as the speed at which the cache and the memory communicates (determined by the chipset), right ? The FSB's fastest frequency is, for now, 266 MHz. What really confuses me is that someone just told me that the fastest communication frequency between the cache and the memory is 200 MHz (not any mobos supports faster...) making PC2100 completely useless with any of the mobos available right now.

I would really appreciate any explanations. Thanks !

Fuzzy Wuzzy was a bear, Fuzzy Wuzzy had no hair...

 

[munkey]

well your friend lied to you SDR-SDRAM goes up to pc-133/266 depending on the mobo. and the pc-2100 memory is DDR-SDRAM. which is very useful if you are running programs with that require a high memory bandwidth.

 

[mpjesse]

Your friend is mistaken. If you want to get technical the current fastest clock speed for a FSB is 133mhz. Now, Athlons and Duron use DDR (double data rate) which effectively send 2 bits per cycle- doubling the bandwidth of the FSB. So, that's why everyone says "200mhz or 266mhz" FSB. The P4 uses a quad pumped 100mhz FSB (four channels each at 100mhz straight to the RDRAM)- Intel likes to call it a "400mhz" FSB. While it isn't actually 400mhz- it is EXTREMELY fast.

Now, on the cache issue- the Duron, Athlon, and P3 (FCPGA)/P4 all have L2 caches that run at the full speed of the CPU.

PC2100 RAM is basically applying the DDR FSB technology the Duron's and Athlon's use. So, you could say PC2100 RAM performs like 266mhz SDRAM.

Get it?

-MP Jesse

"Signatures Still Suck"

 

[HolyGrenade]

THE FSB isn't the CPU's own frequency. It is an acronym for Front Side Bus. This bus connects the CPU to the RAM and the PCI etc.

The CPU's own frequency is the fsb frequency multiplied by the cpu's clock multiplier.


<i><b><font color=red>"2 is not equal to 3, not even for large values of 2"</font color=red></b></i>

 

[hmg57]

Thanks for the eplanations, it seems clearer now. I still don't know why this guy told me that. Maybe it's cause he's Intel biased

Fuzzy Wuzzy was a bear, Fuzzy Wuzzy had no hair...

 

[Guest]

FSB = Front Side Bus. The speed of the FSB (or "bus") determines how fast a CPU communicates with the outside world. Obviously higher is faster. DDR is a technology allowing two bits of data to be sent where only one could be sent using previous technology. This gives (almost) twice the data throughput. The P4's bus uses "double DDR" (my words, not Intel's) which means it can push through four bits of data where only one could go before. Here's the low-down:

Celeron (excp. 800) - 66MHz
Celeron 800 - 100MHz
P3 Coppermine - 100MHz
P3 Coppermine 'B' - 133MHz
Athlon Original/Thunderbird/Duron - 100MHz DDR = (almost) 200MHz
Athlon T-bird 'C' - 133MHz DDR = (almost) 266MHz
Pentium 4 - 100MHz Quad-Pumped = (not quite) 400MHz

PC1600 Memory works at 100MHz DDR, ideally matched to the Original Ath., Thunderbird, and Duron, while PC2100 works at 133MHz, ideally matched to the Ath. 'C'

Sounds like "someone" is out of date by about 6 months. True, there were no motherboards supporting 2100 DDR and 266MHz FSB, but now we have AMD's 760, VIA's KT266 and KT133A (just the bus), and others.

~ I'm not AMD biased, I just think their chips are better. ~