Need Help Understanding System Boards

I thought i had a good understanding of systemboards. But i realized most of the systemboards i worked with only ran cpu's that were 200 mhz and under.

I have noticed that the newer boards are a little different. I used to think that the FSB and the memory bus were the same bus, and i think on the older boards they were. Now the FSB memory bus and clock speed can all be different. Can some one who noes a lot about modern systemboards explain what the main buses on the boards are. And more importantly tell me what there main role of each bus is, and how the different buses interact with each other. I mean like the path data takes to get from one bus to another, and how the buses are layered on the newer system boards.

Also i used to think the clock speed and the FSB speed where always the same speed, and now i no thats not always true. Can some one please explain that to me. I really just want to catch up.

Thanks

I'm not sure if I'm all correct.

My simply understanding is that one PC system has many buses inside, like CPU, memory, PCI and AGP buses and they are all individual buses. They should running at suitable speed. First you must make clear of this.

Suitable speed meaning is that 200MHz CPU using 100 FSB speed, 266MHz CPU using 133 FSB speed, memory also have PC100 or PC133, so you should set your memroy speed to 100 or 133, for 2100DDR memory is equal PC133 speed, so you should set memory speed to 133. For the rest buses like PCI and AGP bus speeds the BIOS will do the job to set their bus speed after you set the CPU and memory speed. Standard PCI and AGP speed are 33MHz and 66MHz. The BIOS just simply asking the clock IC to give the porper bus speed for them.

For example K7S5A board, if you set CPU/memory speed to 133/133 then BIOS will set PCI/AGP speed to 33/66. Other speed setting will over clock or under clock such component and system may not working porperly depand on CPU, memory and other component combination.

PS. Sorry for my bad English.

Hi Panzer676, PANZERA is basically correct. Each bus has it's own divider that works off the FSB. Each bus divides the transfer rate of the FSB to clock down the speed. The AGP, PCI and other components all run off the FSB. They are just running at a divided amount of the FSB. Like the AGP port runs at 66MHZ. When the FSB is at 133MHZ it is running at 1/2 divider. AGP2X is running at 132MHZ because the bus is then double-pumped. And AGP4X is at 264MHZ because it is quad-pumped. When the bus is double-pumped or quad-pumped they can say that it is technically running at a higher speed because instructions are moved on both the rise and the fall of the bus tranfer. So that is a technical increase in speed not an actual MHZ increase. The Pentium 4 has a 100MHZ FSB that has been quad-pumped so they can claim a 400MHZ FSB. DDR memory is the same concept, Pc133 memory that has also been double-pumped. So when you raise the FSB that raises every other bus according to their divider. The PCI slots are basically the same as they have been. There is bus-mastering now so that components can tranfer information without using the power of the processor. AGP (the accelerated graphics port) has a direct access to system memory to allow faster conversions of complex textures for improved 3D gaming. And if you have the K7S5A and the SIS735 you will notice that there is only one chipset. They integrated the north and south bridge into one chip. This allows the board to be 4-layer and cuts cost because only one chip needs to be produced and 4 layer PCB also cuts cost. Also the transfer rate of the north and south bridge are greatly increased because the information does not have to travel through the PCB to get to the other. This is just a basic overview of what has changed but the concept is basically the same.

Ok if everything is run off the FSB speed then what is the 133/133 in bios. When i set it to 133/133 i get memory bus and FSB of 266 and a CPU speed of 1200.

I was told that the 133/133 was some kind of internal clock speed that was not linked to any bus. Or is it that the FSB speed is set from the internal clock, and then every other bus runs off a multiplyer of the FSB speed.

Also if this is true how come there are two internal clock speeds to set in bios?

Thanks for the help so far guys. I really want to understand this stuff.

FSB 133/133 is cpu/memory settings. An example is I have a 1.2GHZ Athlon with a 266MhzFSB(double-pumped). The multiplier is set at 9. If I run my FSB at 100 my cpu would be running at 900Mhz. Multiplier times FSB equals cpu speed. When it is run at 133 the speed becomes 1200Mhz. They allow for seperately adjusting the memory speed on this chipset. The chipset can regulate the fsb and memory transfer speed. The multiplier on the chip uses the fsb and the memory uses the chipset to control speed. In any case the speeds of memory and processor chould be the same or this will cause slowdown because the cpu is waiting on the memory or vise versa.

Ok im getting this. But what is the exact role of the front side bus. Like does data have to go through the FSB if it wants to go from ram memory to the cpu or vise versa. What role does the FSB take with data transfer?

Also what is the internal clock, and how does it effect the system?

And last if the cpu speed is FSB times multiplyer. Then how come the part in the bios the (cpu/memory=133/133) 133 x 9x =1200mhz cpu speed. Which would make the FSB speed 133, and thats the highest you can make it on a normal K7S5A bios. But how come this K7S5A board is supposed to be able to run at 266 FSB at highest.

Or can the FSB run two frequencys, one for the memory and one for the cpu?

Thanks for the info so far mike you are a big help.

Panzera too.

The FSB is the gateway for all of the communications on the motherboard. The data to and from the cpu and memory goes through the northbridge chipset. The southbridge handles controlling components like the pci, agp, and usb ect. The bandwidth between the northbridge, cpu and memory is very fast. 1.2GB per second between memory. The chipset controls the FSB. If you are using the unofficial bios from this site it gives you more settings. Right now I am running at FSB 150/150 so my cpu is at 1.35Ghz(1.2Ghz athlon). The IC(internal clock) is what the cpu and memory use to calculate their speed. Programs like cpufsb change the settings in the IC when running windows. When the computer restarts the IC is reset with the bios settings. When they say this board can run at 266Mhz they mean 133Mhz double-pumped. Data transfer on the rise and the fall of the bus and that makes it twice as fast(266Mhz). The FSB has a setting for the two frequencies because there is memory that cannot run at 133Mhz(Pc100). So if you have an Athlon that runs at 133Mhz FSB and you could not run the memory at that speed then you would have a 1.2Ghz athlon running at 900Mhz. So the chipset allows a clockdown transfer rate between the northbridge and memory. ;)

[yorkie]

Technically it is only 133. As Mike has explained on the AGP, it is double-bumped so the data transfer is doubled.

To understand the concept try thinking of it as a highway. One highway has only one lane, speed limit is 133. Now you're on another highway, which has two lanes, same 133 speed limit. So this new highway has double the capacity of the former one, at 133X2.

About the FSB thing, my understanding is (I may be wrong, someone out that should correct me then) that it only refers to CPU. For some reasons the RAM cannot run at the same speed, say, you got PC100 RAM and a 133FSB CPU, or vice versa, you have to set an suitable clock for the RAM. For example of 133FSB CPU and PC100 RAM, the divider is 3/4. That means when the CPU works 4 cycles, the RAM only works 3 cycles. The north bridge (of course with SIS735 there is no more north or south bridge as they are integrated into one chip) control how the CPU communicates with the RAM. As Mike point out, it is not a efficient way.

Ok i think i almost got this down lol. Tell me if the following is correct.

So the FSB is a bus that connects all the other buses on the systemboard together. With out the FSB none of the other buses would be able to send data to each other.
The FSB can also be called the system bus.
All other buses run at the same speed as the FSB or a divided speed from the FSB speed. Exapt the cpu which runs off a multiplyer of the FSB. But techecnicly the cpu's bus is the FSB, the multiplyer is just for cpu clock speed. So all buses on the system board can only be the same as the FSB or lower. With speed i mean mhz not data transfer.

Also most systemboards have only one FSB speed, but because the K7S5A has to kinds of memory options it allows the memory based part of the FSB to be a lower mhz for the SDRAM(PC100) which is only supposet to be running at 100 mhz. DDRSDRAM (PC266) is supposed to be running at 133mhz but can be forced higher by over clocking.

Ok last questions if i have my board running at 133/133 what is the IC speed? Also can the IC speed be changed like the FSB, and what does the IC speed (mhz) physicly do to the system.

Lastly when you double pump or bump a bus on the system board. How does that make it faster. I understand the highway idea but where do these extra lanes come from. It sounds like you are some how making a 16 bit bus magicly turn into a 32 bit bus. Can you explain this. In other words how does the pumping physicly happen.

Thanks mike and everyone else, you are a great help. I am a Computer Science student so that why i want to no all this stuff.

Ok sounds like your getting it. As far a the FSB being (double-pumped) here is a way to make you understand better. Suppose you have a pile of wood you have to move to the backyard. And so you pick up one piece at a time and take it back there. Then instead of picking up one piece at a time you take two at a time. Keep in mind you are walking the same speed to there and back. But in reality by taking two pieces you should get your work done twice as fast. That is the basic concept. You go the same speed but you do twice the work. On regular PC133 ram data is exchanged on the rise of the bus. On DDR ram it is double-pumped so data transfer is on the rise and the fall of the bus. The IC is what sets the FSB it is the internal clock. The IC can be changed to make adjustments and is reset by the bios on reboot or powerup. I hope that helps you out.