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fsb speed - why does it matter?



 
 
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  #31  
Old November 1st 04, 11:11 AM
Michael Brown
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David Maynard wrote:
Michael Brown wrote:

David Maynard wrote:
[...]

The CPU *does* have a 'multiplier'.



Oooo, you're lucky you put that in quotes :P


It wasn't 'luck'. I use single quotes to denote irony, the 'colloquial
gist' (sometimes akin to irony), or non literal use of a word/phrase.

In that case I was indicating the colloquial gist of the function and
not necessarily a literal.


Perhaps it's a New Zealand phrase I used ... "You're lucky you did
[something]" is often used as an equivalent form to "If you hadn't done
[something] I would have had to do [something else, generally not
positive]". This doesn't necessarily mean that the person didn't forsee
[something else] coming and did [something] to avoid [something else]
happening. In this case the [something else] would have been me upholding my
role as the technicality nit-picker of the group

[...]

--
Michael Brown
www.emboss.co.nz : OOS/RSI software and more
Add michael@ to emboss.co.nz - My inbox is always open


  #32  
Old November 1st 04, 11:52 AM
David Maynard
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Michael Brown wrote:

David Maynard wrote:

Michael Brown wrote:


David Maynard wrote:
[...]


The CPU *does* have a 'multiplier'.


Oooo, you're lucky you put that in quotes :P


It wasn't 'luck'. I use single quotes to denote irony, the 'colloquial
gist' (sometimes akin to irony), or non literal use of a word/phrase.

In that case I was indicating the colloquial gist of the function and
not necessarily a literal.



Perhaps it's a New Zealand phrase I used ... "You're lucky you did
[something]" is often used as an equivalent form to "If you hadn't done
[something] I would have had to do [something else, generally not
positive]". This doesn't necessarily mean that the person didn't forsee
[something else] coming and did [something] to avoid [something else]
happening. In this case the [something else] would have been me upholding my
role as the technicality nit-picker of the group




Oh, it means the same thing in the U.S., except there *is* the element of
'luck' involved whether the casual user realizes it or not, as illustrated
by the companion phrases that don't (explicitly); such as: "good thing you
did that, or else..." and "it was wise of you to..." (although both could
be, and often are, if not usually, used sarcastically to mean 'lucky' anyway).

They are all intros to the respondent going ahead and dealing with the 'or
else' regardless of the 'luck', 'goodness', or 'wisdom' of the original
speaker

The 'good thing' intro can be easily ignored whereas the 'wise thing' intro
might elicit a "thank you" but the common reply to a 'lucky' intro is to
point out it wasn't 'luck', or to admit that it was g.

Your explanation is interesting because I was tempted, but resisted, to say
"and I did it specifically to avoid nit picking replies; which, obviously,
didn't work." g


[...]

--
Michael Brown
www.emboss.co.nz : OOS/RSI software and more
Add michael@ to emboss.co.nz - My inbox is always open



  #33  
Old November 1st 04, 11:59 AM
Richard Hopkins
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"James Hanley" wrote in message ...
memory frequency can be increased to a multiple of the FSB even
before DDR is 'applied'.


Of course it can. Trouble is that you can do what the hell you like to the
FSB:memory multiplier, but after a certain point the connection between the
memory and the processor can't keep up, so your increases in memory speed
are wasted. What is the point of having, say, 8GB/sec memory bandwidth if
the link between the memory controller and the CPU only runs at 4GB/sec?

I have an option in my BIOS to set my DDR-SDRAM frequency,
I can set my FSB to 100 and my SDRAM to 266 (effective).


Virtually all motherboards do this nowadays. However, you are better off
keeping a synchronous memory bus and raising the FSB than you are clocking
the memory bus up and leaving the FSB slower. In both AMD (HyperTransport)
and Intel (NetBurst Bus) cases, the FSB directly controls the speed of the
internal processor to memory bus, and only by keeping the bandwidth of this
bus at least equal to the memory bandwidth can you take full advantage of
the memory speed.

This is why both AMD and Intel have been raising the effective FSB of their
motherboards and processors the last few years. Look at the way Intel went
from 100 (effective 400MHz QDR) FSB to (soon) 266MHz (effectively 1066MHz).
The reason they've done it is to allow sufficient headroom for ever faster
memory to interface optimally with the processor.

So both RAM and CPU can operate at a frequency that is a multiple of
the FSB.
So memory frequency can be increased without increasing the FSB.


Of course it can. The processor bus speed, by contrast, can only be
increased by increasing the FSB.

(i'm assuming bandwidth=throughput, but I cannot check at this moment,
since I'm leaving in a minute, so I have to click Send now!!


For the purposes of this conversation, bandwidth does equal throughput.
--


Richard Hopkins
Cardiff, Wales, United Kingdom
(replace .nospam with .com in reply address)

The UK's leading technology reseller www.dabs.com
Get the most out of your digital photos www.dabsxpose.com


  #34  
Old November 1st 04, 11:59 AM
Richard Hopkins
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"James Hanley" wrote in message
do dabs pay you to post garbage?


No, wasn't sure whether you were genuinely ignorant of the issues here, or
whether you were trolling, so chose to hedge my bets by mildly taking the
p*ss out of you.
--


Richard Hopkins
Cardiff, Wales, United Kingdom
(replace .nospam with .com in reply address)

The UK's leading technology reseller www.dabs.com
Get the most out of your digital photos www.dabsxpose.com


  #35  
Old November 1st 04, 02:34 PM
Richard Hopkins
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"James Hanley" wrote in message
6 years? - but there are loads of articles on unlocking AMD chips,


Try finding one about unlocking Intel CPU's.

i'm sure I think I saw one for the AMD XP 1500+, that's less than 6
years old isn't it?


Read Michael's post again. The six years comment was in reference to Intel
stuff. The only modern Intel CPU's with variable multipliers are some of the
very latest Pentium M's and Pentium 4's, and even there the multiplier can't
be unlocked in the full sense of the word, the chip is shipped with a range
of multipliers accessible.

So how can anybody overclock? Just by upping the FSB to
whatever the mobo supports?


Or whatever the CPU and memory will tolerate, whichever comes first. As has
been said, locked multipliers aren't a problem, as raising the FSB is the
best way to do it anyway.

I suppose that a CPU will have a built in multiplier at a fixed
value


Correct, with the caveat that on many AMD chips, and old Intel ones, it can
be changed by one means or another.

and will assume a certain FSB speed.


Yes and no. The manufacturer, whether it be Intel or AMD, will decide on an
FSB, but rather than the CPU making assumptions, it will *tell* the
motherboard what FSB to select. Most motherboards with any enthusiast
pretensions will be able to override this though.

So if the FSB is lower then it's underclocked. If it's higher
then it's overclocked.


Yes and yes.

Would most people have the FSB at the highest setting suported
anyway,


No way. Most of the people who go out of their way to build an overclocked
system will deliberately choose a CPU-motherboard-memory platform that
offers headroom for overclocking. Intel CPU's are a case in point: the
"slower"/cheaper CPU's with lower multipliers tend to make better
overclocking candidates than the "faster" ones.

Most motherboards will run much faster than their officially supported
speeds anyway. Just look at the old 440BX Pentium II/III chipset, which was
only ever designed to run at 100MHz FSB, but would, in practice, work
perfectly stably at 166 or higher. The situation today is no different.
Intel's Canterwood and Springdale chipsets are designed for operation at
200MHz FSB, but will in practice run at over 300.

(they cna't up the FSB clock because it's already on the highest,
and they can't up the multiplier because it's properly locked)


There's a big difference between the highest speed that's "officially"
supported by a chipset and what it will do in practice. There are also
plenty of examples where you might want to buy a "slower" CPU because it
makes a better overclocking candidate.

btw, Some software tells me that my RAM is operating at a multiple
of the processor speed. I can put my FSB=100 and have 266MHZ
DDR-SDRAM(actual speed 133MHz)


Trouble with this approach, especially on modern platforms, is that setting
the memory bus faster than the frontside bus doesn't get you anything, as
there's a bottleneck in the connection between the memory and the processor,
which you only raise by raising the FSB.

Is it correct that RAM uses a multiplier too?


Yes.

It sure looks like it from si sandra, though there is no option
in the BIOS to set it, I can only set the ram frequency.


It *is* a multiplier, despite the confusing labelling. The "100MHz" setting
corresponds to a 1:1 FSB:memory bus multiplier. The "133MHz" setting
corresponds to 1:1.3333 FSB:memory ratio. One thing to add though is that
you have to be careful with Sandra and taking what she says as gospel, as
like many women, she often misleads and sometimes downright lies.

strange that there's no option in the bios to set the ram multiplier.


It is exactly that option, it's just that your particular motherboard
manufacturer has chosen to present it in a slightly different manner. Many
motherboard makers list it in their BIOSes as what it is - a multiplier (or,
as is often the case, a divider).
--


Richard Hopkins
Cardiff, Wales, United Kingdom
(replace .nospam with .com in reply address)

The UK's leading technology reseller www.dabs.com
Get the most out of your digital photos www.dabsxpose.com


  #36  
Old November 1st 04, 02:38 PM
Richard Hopkins
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"James Hanley" wrote in message
do dabs pay you to post garbage?


No, newbie. Have you ever heard the saying "Ask a silly question and you'll
get a silly answer?"?

At the time I read your post I wasn't sure whether you were genuinely
ignorant of the issues at work here or whether you were trolling, so I chose
to mildly poke fun at you in an attempt to find out.

If, as another saying goes, you don't like the heat, well, you know what to
do. If, on the other hand, you want to learn something, wind your neck in a
little and learn that not all humour is signposted with smileys. In those
circumstances I'm sure you'll learn a lot.
--


Richard Hopkins
Cardiff, Wales, United Kingdom
(replace .nospam with .com in reply address)

The UK's leading technology reseller www.dabs.com
Get the most out of your digital photos www.dabsxpose.com


  #37  
Old November 2nd 04, 02:06 AM
James Hanley
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David Maynard wrote in message ...
James Hanley wrote:
David Maynard wrote in message ...

James Hanley wrote:


David Maynard wrote in message ...


James Hanley wrote:



it seems to me that nobody needs a high fsb. since they could just
push the multiplier really high.

I can see the greatness of ddr since the same speed processor can
read/write twice as much per cycle. (i assume that the cpu has to be
ddr to receive or write double)

How is it you can see the benefit to 'read/write twice as much per cycle'
yet not see any benefit to more of the cycles?


Obviously I see the benefit of more cycles. What do you think I meant
when I said "push the multiplier really high". That increases the
cycles per second.

No, increasing the multiplier does NOT increase the FSB cycles.



I knew that, it increases cycles per second, but just CPU cycles.
So yeah. I just realised that:
Increasing the multiplier increases CPU cycles (not FSB cycles of
course).
Increasing the FSB increases both - that is what hadn't occurred to me
:P


It isn't because of increasing 'both': that's a matter of the CPU
multiplier being locked, or not.


Maybe I wasn't clear with what I meant by both. I didn't mean
multiplier and cpu cycles.

I meant that increasing the FSB increases both the FSB(naturally!!)
and the CPU cycles.

Whilst increasing the multiplier increases only CPU cycles. (the
increase in the multiplier only serves the CPU speed. But increasing
the FSB serves not just the CPU, but the FSB, which is an integral
part of the system)

I think we're in agreement here, as you say
"a processor at speed X will perform better if it also has a faster
FSB (within reason)."
The value of the multiplier only serves to determine the CPU speed.
Unlike the FSB. (actrually for a given cpu speed, a higher mnultiplier
is worse because it implies a lower fsb)

A 1.83 Ghz processor on a 333 Mhz FSB will perform better than a 1.83 Ghz
processor running on a 266 Mhz FSB, whether you accomplish the test by
buying two different processors or using one with an adjustable multiplier.

It isn't as dramatic an improvement as changing the CPU speed (multiplier)
partly because it's offset by the L2 cache.


So if the system supported it(processor was unlocked and very
underclocked) doubling the FSB is better than doubling the current
value of the multiplier.


It depends on what you mean by that.

If you mean taking a processor of speed X on FSB Y and *either* doubling
the FSB *or* doubling the CPU speed then no, doubling the FSB, alone, is
not as good as doubling the CPU speed, alone.

If you mean, as I suspect you do, doing one or the other to end up with the
same CPU speed after it's all said and done, then yes, because a processor
at speed X will perform better if it also has a faster FSB (within reason).


yep

Let's put it to a practical example. I have an unlocked mobile Barton 2400
on a DFI motherboard that let's me adjust everything, so I can run it
overclocked to 2.2 Ghz at 266 Mhz FSB, 333 Mhz FSB, or 400 Mhz FSB (if I
stay at 'standard' FSBs) by adjusting the multiplier accordingly. Which do
you think will give me the best performance?

It's better to have a faster FSB(thus
increasing CPU cycles and FSB cycles) than to have a slower FSB and a
larger multiplier, which would only increase CPU cycles.


You're mixing apples and oranges. In one case you alter the CPU speed but
not in the other.


we must be misunderstanding each other. In both cases, i.e. whether
increase
the FSB or increase the multiplier, it will increase cpu clock speed.

we agree, that for a given cpu clock speed, a faster FSB is better.
The higher multiplier does not benefit the system other than
increasing the cpu clock speed.
For a given cpu clock speed, a higher multiplier would mean that the
FSB is lower, which is actually detrimental.

I'm just saying that for a given cpu clock speed, a higher FSB is
better. Better than a higher multiplier, since a higher multiplier
implies a lower FSB.

That might be a constraint imposed when using a locked
multiplier CPU but it confuses the matter that increasing the FSB, alone,
improves processor performance because more instructions can get to it per
second.


More CPU cycles -- more CPU bandwidth


No. More 'CPU cycles' (all else being equal) --- more instructions
executed per second, assuming it can GET the instructions at that rate.


I agree that a faster CPU is not much good if it can't get the
instructions at that rate. I just thought that the expression 'cpu
bandwidth' didn't take the fsb into account.
I erred there. On googling, I just realised that CPU bandwidth
presumably means the maximum supported FSB bandwidth.

More FSB cycles -- more FSB bandwidth

I suppose bandwidth and throughput are the same thing


Bandwidth is capability and throughput is what is actually going through.


thanks for your response

  #38  
Old November 2nd 04, 03:09 AM
David Maynard
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James Hanley wrote:
David Maynard wrote in message ...

James Hanley wrote:

David Maynard wrote in message ...


James Hanley wrote:



David Maynard wrote in message ...



James Hanley wrote:




it seems to me that nobody needs a high fsb. since they could just
push the multiplier really high.

I can see the greatness of ddr since the same speed processor can
read/write twice as much per cycle. (i assume that the cpu has to be
ddr to receive or write double)

How is it you can see the benefit to 'read/write twice as much per cycle'
yet not see any benefit to more of the cycles?


Obviously I see the benefit of more cycles. What do you think I meant
when I said "push the multiplier really high". That increases the
cycles per second.

No, increasing the multiplier does NOT increase the FSB cycles.


I knew that, it increases cycles per second, but just CPU cycles.
So yeah. I just realised that:
Increasing the multiplier increases CPU cycles (not FSB cycles of
course).
Increasing the FSB increases both - that is what hadn't occurred to me
:P


It isn't because of increasing 'both': that's a matter of the CPU
multiplier being locked, or not.



Maybe I wasn't clear with what I meant by both. I didn't mean
multiplier and cpu cycles.

I meant that increasing the FSB increases both the FSB(naturally!!)
and the CPU cycles.


I knew what you meant.


Whilst increasing the multiplier increases only CPU cycles. (the
increase in the multiplier only serves the CPU speed. But increasing
the FSB serves not just the CPU, but the FSB, which is an integral
part of the system)


Not if you change the multiplier to keep the CPU speed the same. When
you're looking to what 'effect' something has you keep everything else the
same so the 'difference', if any, is the result OF that one thing.


I think we're in agreement here, as you say
"a processor at speed X will perform better if it also has a faster
FSB (within reason)."
The value of the multiplier only serves to determine the CPU speed.
Unlike the FSB. (actrually for a given cpu speed, a higher mnultiplier
is worse because it implies a lower fsb)


'For a given speed' is the point. Yes, a higher FSB, with a lower
multiplier for the 'same CPU speed', is better. Which was the point of the
topic "FSB speed - why does it matter?"

It 'matters' on it's own merit, not simply because it also increases the
CPU speed and 'CPU speed' is not always in the equation. As in, should I
buy an XP3200+ 333 FSB or an XP3200+ 400 FSB? Or, my mobile maxes out at
2400 MHz but, since I can change the multiplier, which FSB would be best:
266, 333, 400?

snip

  #39  
Old November 2nd 04, 07:50 PM
James Hanley
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David Maynard wrote in message ...
James Hanley wrote:

snip
David Maynard wrote in message

snip
Whilst increasing the multiplier increases only CPU cycles. (the
increase in the multiplier only serves the CPU speed. But increasing
the FSB serves not just the CPU, but the FSB, which is an integral
part of the system)


Not if you change the multiplier to keep the CPU speed the same. When
you're looking to what 'effect' something has you keep everything else the
same so the 'difference', if any, is the result OF that one thing.


by increasing one thing, like the multiplier, and nothing else, you
are just seeing the effect of increasing the multiplier. I wouldn't
call that 'keping everything else the same', I would call it 'me
changing 1 thing and nothing else', the result, is that many things
can change. Infact, in the case you mention where you say "if you
change the multiplier to keep the CPU speed the same" there, you are
actually changng the multiplier(increasing it) and the fsb(lowering
it), so you are changing 2 things, that is a bad test. You're
suggesting chnaging 2 things(fsb and multiplier), by talking about
changing the multiplier to keep cpu cycles the same. Yet you then
write of the importance of changing 1 thing only, to see what effect
it has. I must be misunderstanding your paragraph, but it's not
important, 'cos I didn't mean changing the multiplier to keep cpu
cycles the same. I meant changing just the multiplier, thus letting
cpu cycles rise.



I think we're in agreement here, as you say
"a processor at speed X will perform better if it also has a faster
FSB (within reason)."
The value of the multiplier only serves to determine the CPU speed.
Unlike the FSB. (actrually for a given cpu speed, a higher mnultiplier
is worse because it implies a lower fsb)


'For a given speed' is the point. Yes, a higher FSB, with a lower
multiplier for the 'same CPU speed', is better. Which was the point of the
topic "FSB speed - why does it matter?"

It 'matters' on it's own merit, not simply because it also increases the
CPU speed and 'CPU speed' is not always in the equation. As in, should I
buy an XP3200+ 333 FSB or an XP3200+ 400 FSB? Or, my mobile maxes out at
2400 MHz but, since I can change the multiplier, which FSB would be best:
266, 333, 400?

absolutely.
(answer to your rhetorical Q is 400)
  #40  
Old November 2nd 04, 08:47 PM
Richard Hopkins
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"James Hanley" wrote in message
Infact, in the case you mention where you say "if you change the
multiplier to keep the CPU speed the same" there, you are
actually changng the multiplier(increasing it) and the fsb(lowering
it), so you are changing 2 things, that is a bad test.


No you're not. You're evaluating the performance difference inherent in
changing *one* thing (the FSB), because the CPU clock speed stays the same.
You are missing the point of what David is saying - you need to change *two*
parameters to measure the effect of *one* change.

You're suggesting chnaging 2 things(fsb and multiplier), by talking about
changing the multiplier to keep cpu cycles the same. Yet you then
write of the importance of changing 1 thing only,


You're missing the point of changing the CPU multiplier. All it does is
govern the CPU core frequency. If, for example, you ran a CPU at 100MHz x
20, or 133.333'MHz x 15, the result would be 2000MHz, and the integer and
floating point performance of the CPU would be *exactly* the same, allowing
for any point variations in the PLL. Thus, any changes you saw in benchmark
performance would be caused by the FSB change.

I must be misunderstanding your paragraph,


You are.

I meant changing just the multiplier, thus letting cpu cycles rise.


This is where your misunderstanding arises. Let's remind you that your
initial proposal was that FSB isn't, in itself, important. If you tested
this theory by raising the FSB and leaving the multiplier the same, you
would see an improvement in CPU integer and floating point performance, and,
if you didn't change the memory multiplier, you'd see an improvement in
memory performance too. By changing things like the CPU core and memory bus
multipliers, you can evaluate the effect of FSB changes without the results
being clouded by other issues.

which FSB would be best: 266, 333, 400?

absolutely.
(answer to your rhetorical Q is 400)


James, you came into this thread thinking that FSB doesn't matter. The
answer above indicates that you have revised your opinion. Is this correct?
--


Richard Hopkins
Cardiff, Wales, United Kingdom
(replace .nospam with .com in reply address)

The UK's leading technology reseller www.dabs.com
Get the most out of your digital photos www.dabsxpose.com




 




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