FSB vs. FSB Speed

[imported_bcbcbc]

I'm confused by FSB vs. FSB Speed.

CPU-Z says my FSB is 134.0 Mhz. Right below that it says the Bus Speed is 535.9 Mhz.

Currently I have 768 MB of PC 2100RAM. The Mobo will take PC3200 RAM. Is it worthwhile to upgrade to the faster RAM? Or is the FSB too slow to benefit from it?

Thanks

 

[DrMrLordX]

Are you using a Pentium 4? They have a "quad-pumped" bus, meaning that the effective speed is 4 times that of the actual FSB.

When you multiply 134 by 4, you get 536. I doubt you will see much, if any speed improvement moving up from PC2100 RAM, since the RAM is specced to run at 133 mhz. PC3200 is specced to run at 200 mhz, which means you'd have to run your memory 77 mhz faster than your FSB speed to get it at PC3200/DDR 400 speeds. Running your memory bus out of synch with your FSB would tack on a small performance penalty since you're running a P4.

If you were able to overclock your CPU by setting the FSB from 133 to 200 mhz, then yes, PC3200 would make sense.

 

[imported_bcbcbc]

The CPU is an Intel Celeron D 2.66 Ghz--based on the P4 Prescott.

Maybe I'm thick. I don't understand. On the one hand you say the "quad-pumped effective speed" is 536 Mhz. Then you say the PC 2100 runs at 133--the PC 3200 at 200--a difference of 67 not 77 Mhz. Then you mention "PC3200/DDR 400 speeds." What has the 400 got to do with either 133, 200 or 536?

I still don't understand the diff between the 134 FSB and the 536 "effective speed," which CPU-Z labels the "bus speed."

This part I don't get at all: "Running your memory bus out of synch with your FSB would tack on a small performance penalty since you're running a P4." Are you telling me here that upgrading to the PC 3200 RAM would actually degrade my performance compared to the PC 2100 RAM?

I don't know whether I can safely or even unsafely overclock my CPU nor would I attempt doing so until I better understand the whole picture here.

Is there some place someone can refer me where this FSB/RAM thing is clearly explained?

Thanks again.

 

[3chordcharlie]

Your fsb is 133mhz. Since nothing runs at the simple 'fsb' in newer systems, you can just think of this as a 'clock generator' or base speed from which most of your components derive their true operating speed through multipliers.

Your fsb effective speed is like a 4-times multiplier, though technically what it means is that the front side bus can transmit data four times per clock cycle.

Your effective memory speed is 266 mhz (well, 268 in your case), which means the memory bus can transmit twice per clock cycle.

You could use PC3200 ram, which would use a clock speed of 200mhz to get an effective speed of 400 mhz (again, twice per clock cycle). But because the 200/400mhz speed would be totally out of synch with the 133/533mhz speed of your processor's front side bus, you would suffer from latency issues - data from memory would frequently have to wait around for an extra clock cycle or few before the front side bus could send it on to the processor.

The end result is that even though your fsb can handle more data than your memory can dish out, your system will not perform better with faster memory.

You could check and see if your motherboard supports dual channel ram (essentially two memory systems, both running at 266mhz, in your case) which would improve performance.

 

[coldpower27]

Well to sync with a 533FSB effective, you would need Dual Channel DDR-266, or single Channel DDR533 <- that is enthusiast memory though. Over saturating the memory bandwidth though isn't necessarily a bad thing though, having more is better then having less but optimally you want just enough.

PC3200 in Single Channel would provide 75% of the needed memory bandwidth as oppsote to 50% your getting from the PC2100 now. Dual Channel DDR400 would provide 150%.

 

[DrMrLordX]

Originally posted by: bcbcbc

Maybe I'm thick. I don't understand. On the one hand you say the "quad-pumped effective speed" is 536 Mhz. Then you say the PC 2100 runs at 133--the PC 3200 at 200--a difference of 67 not 77 Mhz. Then you mention "PC3200/DDR 400 speeds." What has the 400 got to do with either 133, 200 or 536?[/q[

woops, sorry. 67 mhz is correct here.

DDR400 is just a name for the standard speed of PC3200 RAM. DDR400 refers to its base memory speed of 200 mhz, doubled because DDR can send data twice per cycle. So, DDR SDRAM running at 200 mhz effectively operates at 400 mhz speeds. PC2100 runs at 133 mhz, which makes it DDR266 memory.

I still don't understand the diff between the 134 FSB and the 536 "effective speed," which CPU-Z labels the "bus speed."

Remember that the FSB and memory bus aren't the same thing. The FSB - Front Side Bus - carries data between the CPU and chipset, while the memory bus carries data between the chipset and memory banks. Normally, the memory speed is set to be the same as the FSB, but depending on the bus protocols in use, you wind up with different effective speeds even when the base speeds are the same. On your system:

FSB = 133 mhz
memory speed = 133 mhz
Actual FSB speed = 533 mhz(due to the fact that data can be sent 4 times per cycle or something like that i.e. it's "quad pumped")
Actual memory speed = 266 mhz(due to the fact that data can be sent to and from memory twice per clock)

If you used PC3200/DDR400 RAM, you'd get

memory speed = 200 mhz
Actual memory speed = 400 mhz

This part I don't get at all: "Running your memory bus out of synch with your FSB would tack on a small performance penalty since you're running a P4." Are you telling me here that upgrading to the PC 3200 RAM would actually degrade my performance compared to the PC 2100 RAM?

Yes, there is the possibilitythat you would lose performance overall switching to PC3200. Depending on your motherboard, you may have the option to set FSB to 133 mhz and then memory speed to 200 mhz, which does cause problems on Pentium 4/Celeron platforms in terms of performance. It also caused a small performance hit on Athlon XP systems, but it does not hurt Athlon 64/Sempron/Opteron systems.

I don't know whether I can safely or even unsafely overclock my CPU nor would I attempt doing so until I better understand the whole picture here.

Depends on your motherboard, cooling, and power supply really. But if you wanted to use PC3200 without a performance hit, you'd have to set your FSB and memory speed to 200 so they'd be running in synch. That would overclock your CPU by quite a bit.

Is there some place someone can refer me where this FSB/RAM thing is clearly explained?

Thanks again.

That's the best I can explain it really.

 

[DrMrLordX]

Originally posted by: coldpower27
Well to sync with a 533FSB effective, you would need Dual Channel DDR-266, or single Channel DDR533 <- that is enthusiast memory though. Over saturating the memory bandwidth though isn't necessarily a bad thing though, having more is better then having less but optimally you want just enough.

PC3200 in Single Channel would provide 75% of the needed memory bandwidth as oppsote to 50% your getting from the PC2100 now. Dual Channel DDR400 would provide 150%.

True, given that he's running a Celery system, he might be in a single-channel config which is starving his CPU by running it on insufficient memory bandwidth. He might see some performance improvement by running single-channel DDR400, but he would also lose perfomrnace by using a divider.

 

[imported_bcbcbc]

The Mobo is Gigabyte 8S648XP-RZ. These are the Memory Specs from the manual:

*3 184-pin DDR DIMM sockets, supports up to 3GB DRAM (Max)
*Supports DDR400/DDR333/DDR266 DIMM
*Supports up to 2 unbuffered DIMM DDR 400
*Supports up to 3 unbuffered DIMM DDR 333
*Supports only 2.5V DDR SDRAM

Here's a quote from http://www.sharpened.net/glossary/definition.php?sdram "SDRAM is an improvement to standard DRAM in that it retrieves data alternately between two sets of memory. This eliminates the delay caused when one bank of addresses is shut down while another is prepared for reading. It's called "Synchronous" DRAM because the memory is synchronized with the clock speed that the computer's CPU bus speed is optimized for. The faster the bus speed, the faster the SDRAM can be. SDRAM speed is measured in Megahertz, which makes it easy to compare the the processor's bus speed to the speed of the memory."

If I understand this correctly SDRAM synchs the RAM speed with the CPU bus speed automatically. If so where/ does "out of psynch" enter the picture?

I don't get the distinction between "Dual Channel" and "Single Channel" DDR. I thought all DDR was dual?

My Mobo specs are silent about Dual and/or Single. So I remain at sea on this. Maybe somebody can clarify this for me?

The Mobo does have an "MB Intelligent Tweaker(M.I.T.)" feature that allows a raft of configuration changes in the BIOS. This looks to be something akin to overclocking? I need to learn more about these settings before I change anything. Right now all the settings are the defaults/autos that came with installation. The system is running fine--doing everything I need--no stutters or gliches. Other than the usual Firefox browsing, email, MS Office apps, etc. I do some light graphics, some photo stuff, and music playback/downloads(legal)/CD ripping and burning. I run J. River Media Center through an E-MU 0404 sound card outputting analog to my 2 channel stereo. No gaming. There's about 80GB of music on a 250GB HDD backed up to a second 250GB HDD.

The PSU is a Seasonic S12 380 Watt. This is new and deliciously quiet--120cm fan.

What I'm trying to do here is replace the existing 768MB (512+256) PC2100 with 1GB of the optimum RAM for this Mobo/CPU. I will then use the existing 768MB on the older Mobo with the old P4 Willamette CPU @1.7Ghz in a new/old build for my son.

So the bottom line questions are: 1. What RAM should I buy? Should I buy 1 stick of 1GB or 2 sticks of 512MB? 2. What settings need to be changed in the BIOS to optimize the new RAM? Performance and stability are fine as is. I would like to gain some performance "headroom" but without compromising stability.

Thanks for the help...

 

[DrMrLordX]

A few points:

First off, your motherboard only offers single-channel memory operation, which means you might actually enjoy some performance benefits running PC3200 with a 133 mhz FSB. I don't know if that will be enough to offset the performance hit from running a multiplier.

Secondly, that definition of SDRAM you quoted is horribly out of date. Starting sometime in the PII or PIII days, chipset manufacturers began producing memory controllers that allow you to run your memory and FSB speeds at different rates using what is generally known as a divider. There's a performance penalty when you do this, but it can be done. Using a divider, you could run your FSB at 133 mhz and your memory at 200 mhz, which would help somewhat in that it would give your CPU more of the memory bandwidth it needs. But, there would also be a performance penalty for using a divider.

Given your current motherboard situation, I would not recommend overclocking. You will be limited by the single-channel memory controller on that board.

Single-channel and dual-channel have to do with the amount of available memory bandwidth when you use DDR. DDR = Double Data Rate, and this refers to the fact that you can write and read data twice per cycle with DDR. When you use a single-channel setup, you get the rated amount of bandwidth between the memory controller and memory banks(PC2100 = 2100 mhz memory bandwidth). When you use a dual-channel setup, the sticks have to come in pairs, and the effective memory bandwidth is doubled(PC2100 dual channel = 4200 mhz memory bandwidth). This is very important for P4s and Celerons, but sadly, a lot of Celerons are sold on cheapo single-channel boards.

1). As far as RAM goes, I wouldn't worry about it too much. 2x512MB sticks would be your best bet. Due to current prices, PC3200 DDR would be what you want(PC2100 isn't much cheaper). If you can find a real bargain on PC2100 sticks instead, try that, though they aren't as common in 512MB sticks as PC3200.
2). You could try running your new PC3200 RAM at 200 mhz while leaving your FSB at 133 mhz, which would probably be your best bet. I can't guarentee that this would make your system faster, but it might help a little. Your motherboard manual should have the necessary information on how to do that.

When buying your new RAM, just remember:

PC2100 = DDR266
PC3200 = DDR400

Don't mess with DDR2, that's not for your motherboard.

 

[imported_bcbcbc]

DMLX--

Many thanks. I think I finally got it. I understand now the DDR/DDR2 thing, which was +/- the missing link. Had I understood this a couple of months ago I probably would have bought a DDR2 Mobo. Live and learn.

Fact of the matter, I don't do any "heavy lifting" with this rig so what I got is likely fine...

 

[rogue1979]

Not to be argumentative, but even if you are running a P4 or Celeron at 133 (533MHz fsb) and you use a memory divider to move up to PC3200 from PC2100 speeds, you will realize a significant boost in performance. The P4 platform loves the bandwidth.

With a socket A AMD you will not get any extra performance from using a memory divider to speed up memory speeds past the fsb of the cpu.

 

[imported_bcbcbc]

Rogue--

Are you suggesting I should overclock the DRAM from the current setting of 266 to 400 while still using the existing PC2100? Would this be safe?

I still don't understand the "memory divider?" Is this something built in to the BIOS? Or is it software I have to download/purchase?

My BIOS will let me manually set the CPU clock--100 to 355Mhz. Current setting is 133. The DRAM clock can also be set either auto (default) or manually.

 

[DrMrLordX]

Originally posted by: rogue1979
Not to be argumentative, but even if you are running a P4 or Celeron at 133 (533MHz fsb) and you use a memory divider to move up to PC3200 from PC2100 speeds, you will realize a significant boost in performance. The P4 platform loves the bandwidth.

With a socket A AMD you will not get any extra performance from using a memory divider to speed up memory speeds past the fsb of the cpu.

A fair point. He is starved for memory bandwidth on that single-channel board. Is the expected boost in performance enough to offset the penalty for running a divider?

 

[rogue1979]

Your PC2100 may or may not hit PC3200 speeds. If you have a floppy drive, I would suggest booting to memtest to check memory stability at overclocked speeds first.

I have benchmarked and owned many different P4 systems. While fsb for the cpu is important, memory speed is even more important.

For example a P4 running 667MHz fsb running memory at 1/1 for 333MHz would not be as fast the same speed P4 running 533MHz fsb with a divider to boost the memory up to 400MHz. This is with both cpu's running the same speed. Socket 478 always benefits from raising memory speeds above 266MHz, regardless of the actual fsb speed of the cpu or if a memory divider is used. Of course higher memory bandwidth works better with an 800MHz fsb cpu, but it still increases performance on a 400 or 533MHz cpu.