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Confused by "front side bus"

by NewbieUser2 / September 26, 2004 1:05 PM PDT

I was looking at a Biostar mother board here:

It says it can go up to an 800 Mhz Front side bus. I know this depends on what type of Intel cpu I get. But the specifications state that I'm to use ddr 400 ram. I know that DDR means double data rate. So is this how an 800 Mhz front side bus is achieved? The mother board also supports 533 and 400 Mhz. So does these bus speeds depend on the type of Intel cpu I get? I know different processors have different bus speeds, but I'm trying to understand how the bus works. Thanks in advance. If this is a double post, sorry about that. I thought I posted earlier, but I don't see my post here.

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Re: Confused by "front side bus"
by Mark5019 / September 26, 2004 2:32 PM PDT

best place to ask is the mother boards manafactuer

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Re: Confused by "front side bus"
by JMarchi / September 26, 2004 10:54 PM PDT

If you use 400Mhz memory in matched pairs you benefit from the 800Mhz Bus speed. If you get a processor that runs 800Mhz then you want 400Mhz memory.

The 533Mhz memory is usefull in the new Prescott processors that run up to 1066Mhz with matched pairs of 533Mhz memory. Expect this to be high priced and produce high end performance.

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Intel gets the 800 MHz
by Ray Harinec / September 26, 2004 11:05 PM PDT

by having two memory busses from the MCH [memory Controller Hub] which is their name for what was usually referred to as the Northbridge part of the chipset. The other functions of the northbridge are still in the chip but Intel calls the entire chip the MCH. They call the Southbridge the IOCH .

My understanding is that the two busses are clocked a quarter cycle different in phase so they get four read/writes per clock cycle.

32 bit AMDs only have one bus from the MCH to the CPU. Totally different in their 64 bit CPU's. The MCH in on the same die as the CPU and thus the FSB no longer has any real meaning because it could run at the same speed as the rest of the interior of the CPU. [provided that memory data was available fast enough].

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Don't get this confused with Dual Channel
by Ray Harinec / September 26, 2004 11:11 PM PDT
In reply to: Intel gets the 800 MHz

which uses pairs of Memory sticks, each stick has a memory path to the MCH, to get a double width memory bus. [64 bits by Double = 128 bits]

Faster DDR's than DDR400 are now available, thus the higher FSB's.

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Re: Intel gets the 800 MHz-So how do you determine FSB?
by Brandon Eng / September 27, 2004 12:01 PM PDT
In reply to: Intel gets the 800 MHz

I've looked over this post, did some googling, and still not sure if I understand. My daughter's system has a 2.8 Celeron-D, with a 533 FSB on the chip.

The Biostar P4VMA-M manual say it supports P4 chips w/a FSB of 400/533/800, with support for 266/333/400 DDR mem modules. I have 1 512 stick of pc3200 (ddr 400) installed, the highest rated chip I'm supposed to install.

On bootup, I see "DDR DIMM" 400- I assume this is the pc3200 memory installed. Instructions per clock cycle on Intels is 4 (quad-pumped?")is it fair to say that 4 instructions/cycle X 200 = 800 FSB?? (in the BIOS for DRAM, it says "200 Mhz"- fair to say this is the fastest bus of the motherboard? Or 1/2 of DDR 400=200 (?)

There's no jumpers on this board, except for the CMOS, so there's nothing on the board to jumper re: the FSB. The Award-Phoenix BIOS isn't familiar to me, and there's nothing in the manual that tells me what is what.

And something else in the Biostar BIOS confuses me; in advanced chipset features, for "current FSB frequency" it says 133 Mhz; isn't this something to do with the cpu frequency/multiplier? Is it the multiplier for the cpu? 21 x 133= ~2800. I came up with the 21 by dividing 133 into the chip speed of 2800. Guess my point is, I know there's a relationship with the motherboard bus,cpu, and maybe the multiplier. The fastest bus on the motherboard, among the different busses, directly relates to the external bus, correct? I never really thought about this stuff until I saw this post, and since newbie has a Biostar, my interest is really piqued. That, and I'm curious about Intels, as I've always used AMDs.

Apologies to Newbie for hijacking this thread, but hopefully if Ray or someone comments on this, both of us can get a better understanding. I still can't say for sure I'm running at an 800 Mhz FSB; but I'm assuming I am.

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by R. Proffitt Forum moderator / September 27, 2004 12:10 PM PDT

Let me write a little about that. The numbers are noted in many ways....

For instance the PC3200 (the 3200 part is of interest) is to write that it can supply 3,200 million bytes per second in bursts. Since the stick's memory path is 64 bits, that 8 bytes so 3200/8 = 400 MHz DDR Clock speed. Since both the falling and rising edge of the data clock is used the real MHz on the clock line is all of 200 MHz. shows this as well.

All this can cause one to explode as there is not much to do other than get the right speed memory to match your CPU and chipset.


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Re: 800- Thanks for link; too late to absorb now. But
by Brandon Eng / September 27, 2004 1:25 PM PDT
In reply to: 800

The easy part is matching the memory to the chipset. It's Intel's different external busses that have me confused, and I do try to understand what's going on in my computers. This is my first Intel build in more than 8 yrs, as I'm an AMD fan.

OK, for the sake of simplicity: is it fair to say if you match the correct speed to your motherboard's chipset, and the cpu's external bus meets or exceeds that speed (to achieve a 1:1 synchonization), you'll get the reported motherboard's FSB? In my case, a VIA PM800 w/pc3200 ram.

Was I correct in advising my 'bro in law NOT to get something like a P4 3.0 with an external bus of something...well, it was more than 533, when his motherboard only supports a 133 FSB? I figured it'd be a waste of bandwidth if the board couldn't keep up with the cpu. Do I have that straight at least? Thanks, Bob.

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by R. Proffitt Forum moderator / September 27, 2004 8:54 PM PDT

In short, no. The FSB has nothing to do with anything anymore. The CPUs have been redesigned and the terminology we used before is gone.

Here's what we do now. We crack open the motherboard manual and see what memory we need for that board.

Here's why. There are now multiple busses in the PC design. The old FSB may now be entirely inside the newer CPU and instead the memory controller will present it's own clock system... An interleaved memory controller's FSB rating may be quoted at 2X or even 4X the clock rate that is sent to the memory sticks.


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For the umpteenth time. LOL
by Ray Harinec / September 28, 2004 2:22 AM PDT

Intel has TWO FSB busses from the MCH to the CPU. The MCH pases the two 400 MHz busses to getthe effect of an 800 MHz clock.

AMD only has one.

Your Daughter's does the same thing but is only using 133 MHz memory which by the exact same processes double and double the effective clock rate to 533 MHz.

Remember that 133 is really 133.3333333 a never ending decimal. Take that into account if you try to do the math.

I write these as if it takees one clock to make a memory read or write. If one reads the link that gets to the article on memory latency you'll see that it takes many clocks to make a memory read or write, but it reads a whole batch of memory to get one word, puts the rest in the cache and with ghood luck the next piece of data is in the case and the CPU can get that much faster.

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Hey, gimme a break! I'm not an EE! Just a hobbyist trying to
by Brandon Eng / September 28, 2004 3:46 AM PDT

understand all this! We must have been typing at the same time, (talk about synchronicity, lol) because I didn' see your post before I started on mine.

Where I was still confused in your original post, was when you said, "they get four read/writes per clock cycle." OK, OK, you also said 1/4 cycle; only in hindsight do I understand what you mean.

Sheesh, all this, and I just want to upgrade to a faster system! Newegg has on sale, today only, a P4 3.0 Extreme today for $189. Very tempting, as I've told you my daughter's upgrade bit into my A64 upgrade budget, and you've convinced me socket 939 is the way to go. Financial constraints may force me to go Intel. And for $189, it's very tempting.

btw, when I was talking to the Intel rep, I asked him why there was no press on a 64 bit Intel, and he says they already got 'em. I said, "like Xeon, or Itanium? Gimme a break!" He laughed and said, "well you asked." So I asked for the end user, not some big company, and he hinted that Longhorn will be relesed late next year, and Intel "will be ready." I don't know if he was serious, or just trying to make me an Intel convert, but if Intel was really doing something about a new 64 bit consumer proc, I sure haven't read anything about it.

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Pretty good price for the Intel. Is it retail??
by Ray Harinec / September 28, 2004 5:37 AM PDT

When compared to a 32 bit AMD, Intel is a far safer way to go, for a home builder, because of their builtin thermal protection, and you saw the heat spreader, and better HSF mount on your daughter's.

I'm running a 2.6 on a Gigabyte KN8XP [letters may be reversed] on the Township computer that I built for them. Had to hold to the 2.6 due to budget. Now way could I justify that mobo but Toni had told how much the she liked hers.

That mobo can take a total of 12 drives if SATA included. The feature over the MSI's at that time is that it's RAID controller can be used for ATA or ATAPI drives by selecting them in the BIOS. [MSI's wouldn't support ATAPI.

Some confusing things with these mobo's is that both the SATA and the RAID controllers have their own section of the boot screen. If you have one drive on one of them the boot sctreen shows it and reports "Drive not found" for the other. Of course it didn't find it.

That mobo has a program that reports on the temps and speeds and will even automatically overclock for you in increments.

If you think that you will some day load it with drives, get a server case and a top air exhaust fan. And of course a Proffitt power supply.

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The ground is moving. Can't keep up.
by R. Proffitt Forum moderator / September 28, 2004 5:45 AM PDT
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That's good news. I think that they still only
by Ray Harinec / September 28, 2004 5:57 AM PDT

present the temp diode out to the mobo and it is up to the mobo to calculate the temp and take action.

I have the data on the Sempron, will read it later when my eyes are rested. Also don't know if they automatically throttle down with temp the way that the P4's do.

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Retail, and sale ends today 4PM P.S.T.
by Brandon Eng / September 29, 2004 5:11 AM PDT

It's really tempting, but I've learned from my past history that I've made wrong choices by deciding things impulsively. Still, 3 Ghz, hyper-threading, and an 800 Mhz bus...that should be more than suficient for my needs.

But I need to decide on a motherboard. My existing socket A Asus A7..whatever model board has served me really well. Well, if I really wanted to make my life simple, I could just get a Barton chip, but my FSB would be locked at 333; but we've kinda had that discussion before. I think I'll look at some Barton prices. I'm really sick and tired of upgrading, and being really near-sighted makes it hard for me to read anything off the motherboard.

Since you mentioned RAID, have you seen the latest edition of MaxPC? It seems that RAID as far getting more performance, isn't all it's cracked up to be.

As I've mentioned, I'm not interested in SATA now. So that's a moot point for me as far as motherboards. I've decided to be more minimalist on my next upgrade, whenever that is. I'm sick of looking at all the stuff jammed into my midtower case- 2 HDDs, 2 optical drives, big fat ribbon from Audigy soundcard to external bay, Vid card, tv capture card, and the mass of wires; there's so many connections to the back of my tower, I've taken a picture of the back with the connections to remember what goes where.

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I have ZERO interest in RAID.
by Ray Harinec / September 29, 2004 6:09 AM PDT

Mentioned that article in some other post. You fail to get the points that I've made about raid ports.

If you get a decent mobo it WILL have RAID ports. My point was if you get a mobo with the correct RAID controller those ports can be used for regular hard drives and with the right controller also fo CD-drives.

I know that the Gigabyte mobo that I mentioned has the ITE Gigaraid chip which supports ATA and ATAPI as well as RAID [that is NOT true of all RAID controller chips, need to read the tomshardware articles on each mobo type to find out which mobo's RAID chip supports what]. Don't sneeze at it you can run all of your ATA and ATAPI drives as masters on those mobos. [8 IDE ports, 4 masters]

Don't fight SATA, it's here, any good new mobo has SATA ports and most new Power Supplies have the power connectors for SATA. The next hard drive that you wipe out will be replaced by a SATA [wanna bet?]

I won't try to shame you into getting a Gigabyte mobo. They ARE more expensive, and the cost may not be justifiable.

I enjoy trying to get you into the poorhouse or at least your wife's doghouse. Hope that you have a comfortable couch. LOL

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Hmmph! Glad to see you're feeling better. ;)
by Brandon Eng / September 29, 2004 7:09 AM PDT

If my daughter's system didn't tank, we may not even be having this discussion now. I was all set for the A64 upgrade, agreed w/your suggestion of a 939 socket, and I was all set to go with an MSI board. The Intel build changed the whole landscape (both financially, and rethinking a cheaper upgrade.)

Now all these discussions about busses and all, have made me do some research (as opposed to pretty much blindly following my techies advice). Chipsets, Northbridge, Southbridge, Brooklyn Bridge, aack! My head is spinning, but I do have a much better understanding of what's under the hood. Good and bad. Looking over mobos, there's always a quirk or 2 that's making an informed decision difficult. Even matching up ram to a vendor's mobo is becoming mind-numbing. And I STILL have the Ebay guy's motherboard and chip! I'm tempted to just pop that 2800+ Barton chip in my system, add some ddr 400 ram (but will only run @ 333) and be done with it. OR, I just may swap out some of my hardware into my daughter's system, like the tv capture card and DVD burner. Ever since my daughter's system was "in the shop" so to speak, she's been using my laptop with a wireless adapter. All she does is IM with her friends anyway. Spoiled kids these days!

It must be 3 weeks now going from my "ebay" thread, to my daughter's PC dying thread, to THIS thread that I've apparently hijacked (apologies again to Newbie, wherever you are)- oh, and I have another puter problem that I'm having; my laptop is flaky, and I've been waiting *6 weeks* to send me a new chassis- all this, and all I can say right now, is exhausted from it all.

I've been talking higher end systems for upwards of 3 weeks now (with your help, heh, heh), and I've spent about all my time on the net. Factor that into my decision making, lol.

The next hard drive that you wipe out will be replaced by a SATA [wanna bet?] At this rate, I WONT have SATA, so you lose!

I have about 4 hrs. to buy that P4 3.0 E w/HT. No way am I gonna find a motherboard to my satisfaction. So I guess my next move is to simply wait. I just want to pull the covers over my head and go to sleep! But seriously, I appreciate all your input. Hope you're recovering well.

And stop confusing the issues with facts! Off to newegg again!

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(NT) (NT) To make it worse - new form "BTX"
by billzhills / September 29, 2004 7:14 AM PDT
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Maximum PC showed it in an issue about
by Ray Harinec / September 29, 2004 7:51 AM PDT

two months ago. You may not remember that Intel put out the original ATX spec [with others] that had the power supply fan pulling air in and exhausting it over the CPU to cool it. [the early PII's could run with only a heatsink.] It was touted as a brilliant design. In a few months, as CPU's continued to consume more power, Power Supply and computer mfrs reversed the direction of airflow for the Power Supply fan. The spec got changed about a year and a half later!!!

The BTX really doesn't look like a great Engineering feat for cooling, that is why it isn't catching on at any great rate. For some reason they totally reversed sides so that it gets serviced from the right side. Maybe they don't want anyone to make a case that can be ATX or BTX.

I see nothing good enough about the cooling design to ever warrant going to it. BUT in a while there will be no choice. In my case I'm old enough that I may not have to go to it.

With a top exhaust and a side intake squirting air towards the CPU/HSF, there is no reason to change to a BTX. [other normal intake, exhaust and power supply fans of course]

Just bought a big fancy [way too fancy] server case and started to accumulate stuff to put a mid grade system in it. Procrastinating, so I may unload the Mobo, memory, and CPU,and hard drive. and plan on putting a 64 bit socket 939 AMD system together in it.

Keeping an eye on mobos for it.

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Now to counter some points of mine.
by Ray Harinec / September 29, 2004 6:23 AM PDT

I only explained how Intel gets the 800 MHz FSB. I didn't say that it was better than sex.

Remember many AMD CPU's with 333 MHz FSB outperform the Intels and they are all running at lower CPU speeds.

The architecture of the CPU has so much to do with it, also the amount of L2 Cache [and the architecture of how it is used]. Again, no single architecture is the best for all application programs.

I liked Intel [but talked up AMD because we need someone to keep Intel honest. The old competiton bit] mainly, only because of their superior thermal control and the fact that their chipsets worked right the first time. VIA and even NVIDIA always took two tries. The first buyers were stuck. Their first mobo's claiming to support 400 MHz FSB simply didn't and they wouldn't replace them for those that bought them for that purpose.

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Hope you're feeling as good as you sound!
by Brandon Eng / September 29, 2004 10:38 AM PDT

You ok Ray? Sounds like you're debating yourself <eg>

I only explained how Intel gets the 800 MHz FSB. I didn't say that it was better than sex.
With a prepubescent 11 yr. old girl, and a typical 6 yr. old boy (meaning both are inherently insane), and an incredibly stressful job, I'd say it's a tie, lol.

STILL haven't found a board I like to go with the Intel 3.0 E. I'm gonna miss the sale....

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They'll offer it or better in a week or so.
by Ray Harinec / September 29, 2004 10:57 AM PDT

Have you gone to tomshardware and read the mobo reports for the Intel 875 Chipset mobo's? The articles provide beacoup information about the various mobos. There are a lot to like.

I bought the Gigabytes, one for 220 and the second for 200 in January. The others were all less than 170.

They don't have that one anymore but have a gigabyte for the 875P chipset for 125.

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Missed the sale, no biggie
by Brandon Eng / September 29, 2004 12:19 PM PDT

Cuz it's only about $5 more now. $220 for a mobo? I don't think I've even ever paid $100 for one! I'll take a look at the Gigabyte only on your say-so. Oy, now I have to familiarize myself w/yet another chipset? I'm still partial to Asus though, and that's what I was looking at at newegg a little while ago.

I think I'm gonna have to sit back and take a deep breath and figure out my game plan. Gonna call the ebay guy and ask him again what the heck he wants to do about the chip and motherboard (stinking ECS!). I don't have any legal obligations to return the thing to him, but if I don't pay him for it, bad karma's gonna rain down on my head.

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Where's the beef?
by Brandon Eng / September 29, 2004 2:07 PM PDT

I read through some of the articles on the 875 chipset, and didn't see anything earth shattering.

The one Gigabyte board I saw was the Gigabyte GA-8KNXP. Is this the one you were talking about? I doubt it, cuz the cheapest price was #199. What the heck is a dual-bios?? Never saw that before.

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Re: Confused by "front side bus"
by billzhills / September 27, 2004 7:37 AM PDT
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Re: Confused by "front side bus"
by Brandon Eng / September 27, 2004 1:34 PM PDT

So Bill, does that mean you're running at a 266 Mhz FSB?? Sorry, I'm used to AMD chips, if it says it runs at a 266 FSB, I just get the proper ram to run at the same speed. Intel's P4s seem to do things differently, so I don't know what's what.

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Re: Confused by "front side bus"
by billzhills / September 27, 2004 11:42 PM PDT


FBS is 533 Mhz, on dual channel M/B. Dual Channel M/Bs' allow one memory chip to be read from while the other is written to. Don't ask me to break down the data transfer speed. Its something I understand but not well enough to explain.


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Brandon and Billz
by Ray Harinec / September 28, 2004 2:08 AM PDT

Billz you are confusing Dual Channel with the way Intel gets 200MHz DDR 400 [PC 3200] to 800 MHz FSB. I told it earlier in this thread. Intel has two sets of 400 MHz [200 by 2 DDR] busses between the MCH and the CPU. AMD only has one FSB bus beteen the MCH and the CPU. Intel phases the clocks of the two 400MHz FSB busses to get twice as many DDR reads per clock cycle = 800 MHz. {this is NOT Dual Channel]

Dual Channel is the system where each memory stick [same size, speed et al] has its own memory bus to the MCH. This DOES NOT increase the FSB, it simply doubles the number of bits being input to the MCH.
[it does affect the effective memory bandwidth].

If one looks at a typical mobo that supports Dual Channel for an Intel CPU you will note that there are pairs of memory sockets each pair of memory sockets are a different color. Some have six sockets three of each color. [the gigabyte that used for our Twp computer]

Consider the mobo with 4 memory slots where two slots are Sockts A [memory bus A] and the others are Sockets B [memory bus B]. If you put two sticks of memory in the A Sockets the FSB is STILL 800 MHz, and one stick could be 256 MB and the other 512 MB, no need to match.

If you,instead, put one stick in an A channel slot and one in the corresponding B channel slot [in this case the two memory sticks must be of the same size, called matched, but only need to be matched in speed and amount of memory on the stick].You will then be running dual channel and the FSB WILL STILL only be 800 MHz. but the data bus [memory bus will be 64 bits wide rather than 32 bits.

It is the same with AMD mobo that supports a 400 MHz FSB and Dual Channel [only thing different for many of them is that they only have THREE memory slots. To run Dual Channel you put one stick in color A and one in color B [matched sticks], then you are in Dual Channel and the FSB is only 400 MHz. Put two sticks in the same color slot and you are NOT in Dual Channe mode BUT the FSB is still ONLY 400 MHz.

Let's not bring in those CPU's system that have the MCH built into the CPU. For those the FSB is essentially meamningless because its upper limit would be the same as the speed that the CPU runs internally.

I note that some of the links given in thread have some rather dated information.

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Re: Brandon and Billz
by billzhills / September 28, 2004 2:42 AM PDT
In reply to: Brandon and Billz

Thanks Ray,

Reread my post and I was confused.

Increase of tne memory bandwith was what I was after.

And the links are dated for today systems,
wiil have to find newer sites


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Re: Brandon and Billz-OK, I think I have it now.
by Brandon Eng / September 28, 2004 3:17 AM PDT
In reply to: Brandon and Billz

I called Intel's customer support: 1-800-538-3373.

The guy was nice enough, but at first spoke to me like a total idiot. I told him I have a P4 2.8 Celeron-D w/533 built-in bus.

I asked him what FSB I'm running at. He asked what type of ram I used, and told him ddr400 (I deliberately didn't say pc3200; sounds too technical. I may be confused, but I'm not an idiot, and wanted him to explain to me things in simple terms.) He said then I'm running at a 533 FSB, and to prove it, he directed me to an area in Intel's website to d/l a utility that gives info on the chip. I did, and he directed me to an area in the utility and asked me what I saw. I said "533". "Voila!" he says.

So I said, now wait a minute, are you telling me my SYSTEM MEMORY is 533? (tipoff that I wasn't a total dope.) Pause. Then he starts talking all techno-geek stuff; either to make me shutup and go away, or attempt to further confuse me. He also added he was A+ Certified. Whoopdeedoo.

So I say, look, I know my *system* memory is now 133 Mhz. Using DDR ram, effectively doubles that, can we agree on that? He says yes. So I say, your current P4s send 2 instructions per clock cycle/apparently *2* busses, and in conjuction with ddr ram, that's where Intel's "quad-pumping" gives you an EFFECTIVE FSB of X speed, depending on the built-in FSB of the P4s, using 4 as a multiplier of the system memory. He says he never heard of quad-pumping! I suspect Intel doesn't like the term anymore, so he was denying any knowledge of quad-pumping. Then he says a motherboard has many different types of busses. I said, yes, I know, the pci, agp have busses, but I'm talking about the SYSTEM BUS, the fastest bus that communicates with the cpu (I think he finally realized I'm not totally brain-dead.)

Then I say that we've agreed that ddr ram effectively doubles the system bus, in my case, 2 x 133=266. Then I ask can we agree that Intel P4s sends 2 instructions/clock cycle (he said he didn't know anything about 2 busses), effectively doubling the system bus. He says yes. Then I say for the sake of simplicity, to determine my FSB I simply multiply 4 times the system memory, correct? So 4 x 133= ~ 533, which is, for all intents and purposes my FSB. I don't know why he sounded so reluctant to respond, but he finally said, yes, I'm correct. I think Intel doesn't like the terms "effective", "quad-pump", and not once did the guy mention AMD- he said "another manufacturer", lol. And it was he who mentioned "the other manufacturers" single bus.

So tell me I've finally got it Ray! And to Newbie, apologies if I've seemed to have hijacked your thread. I'm hoping both of us can learn something from this. And for further clarification, I'm speaking ONLY about Intel P4s, NOT any flavor of AMD, nor dual-channel memory.

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Yes you got it. Interesting that
by Ray Harinec / September 28, 2004 3:48 AM PDT

that they don't use the term "quad punmping" any more. Back when they first used it, the explanation that I found was that they artificially created a second buss [virtual bus]. They needed to double the number of clocking opportunities each cycle. With a normal rectangular wave clock waveform, one only has the leaing and the trailing edge to use to clock data in. By creating a second bus shifted from the first by 1/4 of a cycle they got the extra two clocks per cycle they needed. Exactly how they created this "second" I never exactly found out. I assume that somehow the MCH creates it.

I think that I have a PDF with the CPU pinouts. Small print and I juat had a cataract removed from left eye this morning and still can't close my right eye from previous surgery, I may wait a few days to get into small print.

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