FSB, System Clock And RAM Speeds - Confused?

[Beno]

If any1 can help me out with any 1 of these Q's, then this would be greatly appreciated. -> ->

I am confused when I read statements like this:

"We test EIDE hard drives in a PC with a 600 MHz PIII CPU and a 133MHz FSB with 128MB SDRAM..............."

Question 1

First of all when they talk about 128MB SDRAM - Is that RAM in synch with the system clock or the CPU??
Does this mean if I have a 50MHz sys clock that it will be in time with that?? i.e -> operating at 50MHz? If it is DDR-RAM does this mean the speed will be at 100MHz??

Question 2

When they talk about 133MHz FSB - Does this mean the bus speed between CPU, Chipset and RAM is at 133MHz?? If so, then doesn't this contradict the memory speed of the 128MB SDRAM which could be possibly at 50MHz???

Question 3

They have stated in this "Smart Computing" magazine that I have that EIDE interface can handle drives up to 8.4 GB in size. What type of interface is used for the much larger drives with capacities such as 40GB and 80GB??

Thanks for helping me understand :-)

Beno

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Have a nice day

[JadedC36]

Beno;
First I believe 'system' bus, and 'front side bus' are the same. It is the bus from the 'North Bridge' to the cpu socket. The cpu needs a certain clock frequency to operate at it's rated frequency (I will use the P II, and P III for examples). For instance a P II 266 Mhz can only run at 266 Mhz on a 66 Mhz fsb because its multiplier is 4. If you increase the system clock to 100 Mhz then the PII 266 would be a PII 400 and would probably go up in smoke. Currently all system busses are either 100 Mhz, or 133 Mhz. The memory bus is a seperate bus from the North Bridge to the memory sockets (DIMM's), and on most chipsets is adjustable to either 100 Mhz, or 133 Mhz. So you could have the fsb running at 133 Mhz, and the memory bus running at 100 Mhz. The "North Bridge" controls the flow of data to and from the cpu, and to and from the memory, and to the AGP video card, and to and from the other periphals (PCI cards, ISA cards if you still have them, the drives HDD, FDD, DVD, CDR etc., and the PS2 ports for the keyboard, and mouse), and is in some ways more complex than the "CPU".
The 128 MB SDRAM is the amount of memory, not the speed of the memory. SDRAM comes in 32MB, 64MB, 128MB, 256MB, and 512MB sizes,(and possibly 1024 MB) so 128 MB could be 4 32MB's, or 2 64MB's, or 1 128MB. SDRAM comes in 2 speeds, either 100 (PC100), or 133 Mhz (PC133). (note: you can still find SDRAM in 66Mhz modules).
The size of HDD that can be used (recognized) on the "EIDE" depends on the BIOS. The BIOS of older systems that can only see 8GB drives, may be able to be updated to a newer version via a BIOS flash, (or they may not).
I'm sure that if you read this very slowly, and a number of times, it will make sense. I appologize for all the (parenthisies)!

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Mike

[This message has been edited by JadedC36 (edited 12-30-2001).]

[BigBlue66]

Hey,

SDRAM will run at the speed of the FSB of the motherboard. There are at least three speeds of FSB right now, with faster speeds to come I'm sure. Maybe the already have. http://www.PCGuide.com/ubb/confused.gif They are 66Mhz, which is going, or has gone the way of the dodo, and either 100Mhz or 133Mhz.

As mentioned, the RAM will run at whatever speed the FSB is. For example, if you have PC100 or PC133 on a 66Mhz FSB system, then that's all the faster the RAM will run at, ie. 66Mhz.

If you have PC100 on a FSB of 133Mhz, the speed of the RAM will remain at 100Mhz, because that's the speed at which it is rated.

If you have PC133 on a FSB of 133Mhz, then you're in luck because the RAM will be running at its rated speed.

However, if you have PC133 on a FSB of 100Mhz, the most the RAM will run at is 100Mhz because of the FSB limitations. Confused yet?

As for the FSB speeds and the CPU, most if not all systems nowadays use what's known as Double Date Rate or Quad Data Rate (Not sure of the latter terminology) transfer technology. AMD CPUs come in two flavors of FSB speeds, either 200Mhz or 266Mhz. The FSB is effectively doubled at the CPU level, so that a motherboard with a 100Mhz FSB can be used for a 200Mhz FSB CPU. Or, a motherboard with a 133Mhz FSB can be used with a 266Mhz CPU. However, a 200Mhz CPU won't work on a 133Mhz FSB motherboard, because of course the FSB is doubled to 266Mhz, thereby overworking the CPU to the point of not working at all.

Intel CPUs are a different story, and I'm not qualified to tell you much about them. I'm probably not qualified to tell you anything about AMD CPUs either, but I gave it a shot.

Intel based motherboards, at least some of them, use different multipliers than the AMD ones. For example, I have at work a Pentium 4, 1.7GHz processor with a 400Mhz FSB. The motherboard that it's on is a 100Mhz FSB that's quadpumped to allow for the 400Mhz P4 CPU.

There, are you confused now? I know I am. http://www.PCGuide.com/ubb/biggrin.gif

Hang tight for some other answers. There are a few on this forum that can explain it much better than I.

Cheers,

Big Blue 66


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Once I thought I made a mistake, but I was wrong.

[Beno]

Thanks JadedC36 and BibBlue66 for your responses.

BigBlue -> You said that your FSB runs at a speed of 400MHz on a 100MHz board becuase it has been quadpumped. What quadpumps it. Is it the multiplier circuitry quadpumping the 100MHz system clock??

"If you have PC100 on a FSB of 133Mhz, the speed of the RAM will remain at 100Mhz, because that's the speed at which it is rated.

If you have PC133 on a FSB of 133Mhz, then you're in luck because the RAM will be running at its rated speed. "

When you talk about PC100 and PC133 you are referring to the speed of the system clock aren't you??

Thanks for all your help - - - - - I really appreciate it.

Hopefully some genious like Paleo Pete will write a response up here soon.

Cheers

Beno




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Have a nice day

[JadedC36]

Yes you are right BigBlue66, there is still a 66Mhz fsb, which is going the way of the 33Mhz fsb, and eventually the Dodo. I didn't mention it because it is nearly extinct. That leaves us with the 2 current clock frequency's being used, the 100, and 133 Megahertz Frequency's. The P4 uses the 100 Mhz fsb, but the chipset, and the cpu exchange 4 bits of data with each cycle of the clock, 100 million times per second. 4 bits times 100 Mhz=400Mhz. "quad Pumped" in marketing hype. The AMD 200, and 266 Mhz fsb's are 100, and 133, but the chipset, and the cpu can exchange 2 bits of data (on each wire of the bus) per clock cycle,2x100=200, 2x133=266. Now I admit that I do not know any details about any of the AMD chipsets, but I have done some research on the Intel chipsets, including those by VIA, and I'm reading out of the Asus TUSL2-C User's Manual right now, and it says that I can clock the cpu at 66, 100, and 133 (actually anywhere from 64 MHz, to 160 MHz), and the Memory at 100, or 133 (actually from 99.6 MHz, to 160 MHz). The chipset determines what frequency goes to the cpu, the memory, the AGP, and the PCI (or as in the case of some newer chipsets the "ilink" or "some other cute name for the bus between the north, and south bridges"). Now quite possibly the chipsets for the AMD will only allow you to use a specific memory speed with a fsb speed, I wouldn't know. But I do know that pc100 memory will most likely not run at 133 MHz (some possibly will, but it will be equal to pc133 if it performs adequately at 133 MHz, it will not run at 100 MHz if the bus is clocked at 133 MHZ). Thank you.

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Mike

[iisbob]

Not a bad explanation JadedC36 but the memory bus is actually 32bits wide { or 32 wires if you prefer }-running at a transfer rate of 100-133 million cycles per sec-with each wire handling handling 8 bits of data ( or one word size ) per " tick " of the quartz crystal commonly referred to as the system clock. DDR doubles this by transfering data on the rise andfall of the clock-esentially giving you a 64bit virtual bus width with a perceived speed of either 200 or 266 mhz depending on the actual rated bus speed of the motherboard.

Not even the old 8088's transmitted less than 8 bits per cycle. http://www.PCGuide.com/ubb/tongue.gif


The reason you can use only one RAM module now, instead of the pairs of SIMMS you used to have to run is because they increased the memory wires ( these are actually the buses ) so that you could use a 32bit module.

This addtion of address/memory wires also increases the capacity of memory a motherboard can handle; ie.. the no# of RAM and greater size RAM modules you can place on it.

Currently the memory { or address } bus is still only 32 bit's wide, whereas the data bus and control bus are both 64 bit-when they finally give us a true 64 bit memory width ( bus ) then you'l finally see the removal of one of the main bottlenecks in your system, ( the harddrive is the main bottleneck currently ).


As for the rest of the explanantions here, they all pretty much hit the nail-just remember that when you are overclocking on current systems, by increasing the FSB-you're also increasing the Bus speed of system peripherals-these are controlled by what's commonly termed the " Northbridge " , and PCI cards ( AGP is still a PCI slot, just dedicated to video with a straight pipeline to system RAM ) DO NOT like to be run over their perscribed bus speeds! ( 33 mhz for standard PCI cards; 66 mhz for your average AGP video card )


Hopes this helps you a little. http://www.PCGuide.com/ubb/smile.gif



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iisbob

Life of a tech-support specialist-
"..Tech Support: "Use the right button to click on the shortcut--"
Customer: "I don't have a right button."
Tech Support: "You should have a right button."
Customer: "I'm sure. I have 'ctrl', 'alt', 'backspace'..."

[JadedC36]

Thank you Bob;
I am sorry, I did not mean to imply that the either of the busses consisted of only one wire. I was not trying to convey bandwidth, only the clock speed of the different busses, all of which are controlled by the chipset. I do, however, dissagree that each conductor transports a byte. 100MHz bus, 64 bits wide, = 64 bits per cycle, unless DDR, or Quad pumped. I feel that we have only added confusion to Beno's questions, and for this I apologize.
Edit: The 64 bits is refering to the FSB, the memory bus, I know is only 32 bits wide.
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Mike

[This message has been edited by JadedC36 (edited 01-01-2002).]

[iisbob]

do, however, dissagree that each conductor transports a byte

Now that i reread my post i realize i didn't explain it right, whoops!

Try this; there are 32 wires on a memory bus, each wire transmits a bit-you have 16 on, and 16 off ( 1's and 0's again ), this gives you your 32bit bus width. Now you take that wire and you transmit data on the outgoing { fall }and the incoming { rise } signal-hence DDR.

So you are actually getting 2 bytes per " tick " or 4 in a DDR system.

Now these transmissions don't happen in a straight line-and you have them occuring in millions of cycles per sec, staggered across the memory bus. Every other wire acts as a ground to it's neighbor, then in turn becomes a transmitter.

Make a little more sense? http://www.PCGuide.com/ubb/smile.gif





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iisbob

Life of a tech-support specialist-
"..Tech Support: "Use the right button to click on the shortcut--"
Customer: "I don't have a right button."
Tech Support: "You should have a right button."
Customer: "I'm sure. I have 'ctrl', 'alt', 'backspace'..."

[This message has been edited by iisbob (edited 01-01-2002).]

[This message has been edited by iisbob (edited 01-01-2002).]

[Beno]

Hey guys,

I think BigBlue66's one and only answer is as good as any, but the other responses are good as well. If I think about it too much then I lead myself to even more confusion, but its great how one post can cause a lot of interest..................nice work!! :-))

Cheers

Beno

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Have a nice day

[Hobit]

Bene beno,

BigBlue66 has proffered you valid information with the exception of part of the response to your first question. BigBlue66 stated that "If you have PC100 on a FSB of 133Mhz, the speed of the RAM will remain at 100Mhz, because that's the speed at which it is rated." It probably would NOT run at all. Notwithstanding, PC100 RAM is capable of running at higher than 100MHz - how much higher depends on its quality.

Overclockers, say with a Celeron processor that has a FSB of 66MHz might install either very high quality SDRAM, or PC100.

For example if I had a Celeron 300 with a 66MHz FSB I might overclock it using a multiplier that would increase the processor to 450MHz which in turn would proportionally increase FSB to 100MHz. Obviously PC66 SDRAM would not be stable but PC100 would run just fine.

Hope this is clear,

Hobit

[Beno]

Hi Hobit,

Yes its all clear to me now.

Thanks for replying to me with that info.

Beno

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Have a nice day

[BigBlue66]

Originally posted by Hobit:
BigBlue66 stated that "If you have PC100 on a FSB of 133Mhz, the speed of the RAM will remain at 100Mhz, because that's the speed at which it is rated." It probably would NOT run at all.
Hobit

Boldface type, mine. Not sure if I agree with this or not.

I was lax in my answer, I know, because I only gave bits and pieces of answers, so as not to confuse the issue too much.

There is one thing that I left out, which is something I shouldn't have. And that is, on many BIOSes nowadays, there is an option to run the memory at either FSB or FSB +/- 33, so therefore, if the FSB is 100Mhz, you could effectively run the memory at either 100, 133, or even 67Mhz. With these options, you could come up with all sorts of ways to run various speeds of memory on various speeds of front side bus.

I'm sure if I forgot something, Hobit will jump in and correct me. http://www.PCGuide.com/ubb/biggrin.gif

Cheers,

Big Blue 66


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This space reserved for highly intelligent observations and witty remarks.

"From up on the roof top there came such a clamor, I ran to the window and threw up"
-- Tommy Smothers

[iisbob]

What you have to remember here is that memory speeds are ratings; ie..they are released by the manufacturer at the rated speed of 66,100, or 133-when in actualality they usually are capable of running faster.

The FSB doesn't truely run at 66, 100, or 133-it's more of a 3-5% difference in actual speeds, for instance; a 66 FSB actually runs anywhere from 62-71 MHZ, depends on the crystal's stability and mobo's manufacturer quality. If you have quality PC66 SDRAM it will run on a 100 system bus, i've done this with Micron sticks in my old Gigabyte intel chipset board, ( of course i'm now using PC100's for stability ), it ran quite well for several months until it then began to slowly accumalate more errors so i eventually changed it.

The point is, go for a faster speed rating than what your vendor's motherboard asks for; you'll then have a buffer against possible error's.




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iisbob

CPU= 5mhz
Memory= 16 K
Storage=10.2MB's
Video=Onboard S3 4K
Modem=14.4 baud
Sound=ISA Yamaha 8bit
Mouse=2 button MS
Monitor=ACER 12.5"
OS= WIN 3.1

My ultimate gaming system :)

[Hobit]

Cheers Beno,

Response to your question(s) is made difficult both by the differing RAM types in the market and as BigBlue66 points out the complexities of different bios and differing bios settings for both processor speed and FSB.

Notwithstanding, perhaps the following will clarify. The numbers manufactures use is a guarantee that the RAM regardless of type will function properly at a particular FSB.

ERGO:

SDRAM (168pin) is available as:
PC 66 = 66MHz FSB
PC 100 = 100MHz FSB
PC 133 = 133MHz FSB
PC 150 = 150MHz FSB (Used by overclockers.)
(PC 150 is probably no more than very high quality PC 133 that
Manufacturers guarantee to run at 150MHz FSB.)

DDR DRAM (184 pin) is available as:
PC 1600 DDR = 100MHz FSB
PC 2100 DDR = 133MHz FSB
PC 2400 DDR = 150MHz FSB
PC 2700 DDR = 166MHz FSB (Used by overclockers.)
(Why manufacturers don’t call this type ram which is theoretically at least double rate, PC 200 DDR for 100MHz FSB, and so on is beyond me. Perhaps they thought it might sound more impressive for marketing purposes.)

RDRAM (AKA) RAMBUS (also 184 pin) has been available as
PC 600, PC 700 and PC 800
Is currently available as:
RDRAM 800 = 200MHz FSB
(This is proprietary RAM in that it is only compatible with Intel chipsets and P4s that support a 200MHz FSB. Here the 800 designation makes a little more sense, as theoretically at least this ram is quad rate. )

Final Note: Neither double rate in the case of DDR or quad rate in the case of RAMBUS for whatever reason have not resulted in significantly improved performance over SDRAM dispite all the marketing hype.

God, have I made any mistakes?

hobit

[iisbob]

Final Note: Neither double rate in the case of DDR or quad rate in the case of RAMBUS for whatever reason have not resulted in significantly improved performance over SDRAM dispite all the marketing hype.

God, have I made any mistakes?

Yep, that's the most glaring one i've seen yet.

Anyone who's used standard SDRAM systems, and DDR systems-overclocking or not , can tell you there is a significant difference in performance. if there wasn't what would be the point of using the new technology?

DDR is named based on it's data transfer rate; ie PC2100 means 2.1GB's per sec data transfer rate. Go here, Crucial (http://www.crucial.com) for more info.

Normally i don't rely on test programs to check on my systems performance, but i did run MadOnion on my old SDRAM 150mhz PC133 system ( OC'd just a little ) and on my PC2100 DDR board ( also running at 300{ 150 } ) and there was a a significant increase in performance.

Old system w/PC133=5460 points

New DDR system w/PC2100=9210 points

Major difference.

I hope that was just a quote you saw in some uniformed magazine.





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iisbob

CPU= 5mhz
Memory= 16 K
Storage=10.2MB's
Video=Onboard S3 4K
Modem=14.4 baud
Sound=ISA Yamaha 8bit
Mouse=2 button MS
Monitor=ACER 12.5"
OS= WIN 3.1

My ultimate gaming system :)

[Hobit]

Excuse me Beno this is really in response to iisbob's comment but may I hope serve to further your understanding.

hobit's
Final Note: Neither double rate in the case of DDR or quad rate in the case of RAMBUS for whatever reason have not resulted in significantly improved performance over SDRAM dispite all the marketing hype.
God, have I made any mistakes?

iisbob's comment:
Yep, that's the most glaring one i've seen yet.
Anyone who's used standard SDRAM systems, and DDR systems-overclocking or not , can tell you there is a significant difference in performance. if there wasn't what would be the point of using the new technology?

On the website anantech.com titled-
Cmputex 2001 - Intel & VIA Pentium 4 DDR Chipsets Revealed
Dated June 4, 2001 by Anand Lal Shimpi-
there is a chart that illustrates a 15% increase in overall normalized performance between PC133 and DDR266 (AKA PC2100).

This is, as iisbob points out, a significant increase in performance which warrants their use.

However, it is NOT the increase in performance that the numbers PC133 vs. DDR266 might lead an uninformed consumer to believe. Nor does the 25% increase in performance of PC800 RDRAM over PC133 reflect the numerical difference in marketing nomenclature either.

Beno, hope this exchange has not confused you,

hobit