t4h

Distinguished
Jun 18, 2001
35
0
18,530
Sharky Extreme's guide to P4 oc was great, except for this part:

<-quote-><font color=red>
Most Pentium 4 owners will be forced to manipulate their front side bus to overclock, since the frequency multiplier is locked. Generally, the biggest limitation to front side bus modification is the RDRAM's frequency, which doesn't like to be pushed above 900MHz. With a 133MHz bus, we'd be clocking the memory at 1066MHz - far above the accepted tolerance for RDRAM. For this reason, ASUS has incorporated an extra setting into the BIOS of the P4T to allow the Rambus memory to run at a lower ratio (3x, as opposed to 4x the FSB speed).

Using this feature, we were able to take our front side bus up from 100MHz to 130, 133, and even 150MHz! Since these values are all multiplied by four (after being quad-pumped), our final bus frequencies are effectively 520, 533, and 600MHz!</font color=red>
<-end quote->

I simply can't do the maths. Here's where I loose it:

<font color=red>"With a 133MHz bus, we'd be clocking the memory at 1066MHz"</font color=red>
133x4=532, not 1066!

<font color=red>"ASUS has incorporated an extra setting into the BIOS of the P4T to allow the Rambus memory to run at a lower ratio (3x, as opposed to 4x the FSB speed).

Using this feature, we were able to take our front side bus up from 100MHz to 130, 133, and even 150MHz! Since these values are all multiplied by four (after being quad-pumped), our final bus frequencies are effectively 520, 533, and 600MHz!"</font color=red>
multiplied by four? didn't they just lower the ratio to 3x?

Now clearly, as you can see, I'm having a hard time grasping this, could somebody pleasse explain? BTW, do I set the FSB in BIOS (my mainboard is an Asus P4T (yes, honestly!))?

---
/ Topaz
 

wapaaga

Distinguished
Jan 18, 2001
1,070
0
19,280
yeh frist th9ng you have to look at is the fact that the chip orginal put out a 400mhz bus and it is using an 800 mhz rdram chip the fact that it is using a dual channle means that the four becomes a 2 and 400 *2 =800

so with the 3 setting it is going to run at 1.5 times the speed of the frontside buss
or if you have the it overtclocked to 150 then
150 x 4( for the quad pumping that happens on the chip)=600
x1.5(becuase multipler is set to three)= 900
which can be reached


"With a 133MHz bus, we'd be clocking the memory at 1066MHz"
133x4=532, not 1066!

to this the fact that with a setting for the memory of 4 you have to double it effectively getting 1066

you hvae to rember that the chip is quad pumping it iwhich will cause it to go the fasb to multplyed by 4 irst then the memory timming number
 

t4h

Distinguished
Jun 18, 2001
35
0
18,530
Whoa!

Look at these calculations:

150 x 4 = 600 (quad-pumping)
600 x 1.5 = 900 (ratio at 3x, dual channeling making it 1.5x)
900MHz bus for the RDRAM, acceptable.

150 x 14 = 2100 (150 being the FSB and 14 because 1.4GHz)
You're actually saying that a P4 1.4GHz could be clocked to 2100MHz clock frequency?!

A shame though, it surely isn't very stable, I have numbers that 1.6GHz being the max clockable limit of a P4 1.4GHz, can anyone confirm that? How hot does the CPU get @ 1.6GHz?

---
/ Topaz
 

juin

Distinguished
May 19, 2001
3,323
0
20,780
Look
FSB
4*100= 400
3*133= 400
4*122= 448
Core speed

15*100 =1.5 ghz
15*133 =1.995 ghz
15*112 =1.680 ghz
Keep in mind that you must change setting of PCI.
That rough theory.Most of P4 have been o*c (if overclock) to 112 FSB
 

t4h

Distinguished
Jun 18, 2001
35
0
18,530
Well, say that I would change the FSB to 112 (giving me 1568MHz), what would I set the clock frequency in BIOS for?

How does the AGP and PCI buses get affected by a FSB @ 112? How do I correct it?

---
/ Topaz
 
G

Guest

Guest
at 133mhz on the asus p4t the pci clock is set to 1/4 making it run exactly at spec.
1.3ghz p4 should do 1.72ghz@133fsb
 

wapaaga

Distinguished
Jan 18, 2001
1,070
0
19,280
go look at the in the overclocking form i put a page in there form asus that has all of the jumper setting and how the agp reacts on it
 

t4h

Distinguished
Jun 18, 2001
35
0
18,530
Sorry wapaaga, but I don't understand a word of waht you are saying, could you express yourself more clearly please? It sure seems like an interesting thing you had there...

---
/ Topaz
 

wapaaga

Distinguished
Jan 18, 2001
1,070
0
19,280
<A HREF="http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&p=635122#635122" target="_new">http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&p=635122#635122</A>
 

t4h

Distinguished
Jun 18, 2001
35
0
18,530
Great waggpaa, I appreciate all your help, I've prepared another question for you in the overclocking form... :)

---
/ Topaz