Figuring out Memory speeds vs FSB speeds

[viperdude152]

Damn. You guys know your stuff. I am SOO far behind! haha. I have a home built computer that I built when I was 14, im 21 now. It was a AMD 266 with 64mbs of ram with a 4mb Trident AGP 4x card at the time. I swapped the motherboard to one from TYAN Motherboards and I have a Slot1 intell P3 550 CPU in it with 512MBs of ram and a MSI AGP 8x Geforce4TI4200 graphics card. My motherboard only goes to 4x. I later swapped the mobo out again for the same one since I was having problems but for some reason this board stays at 2x for the AGP even after configuring the bios and updating drivers. Maybe I will swap my old MB back in. I did recently today put a PCI Ultra100 car in so my hdd can work closer to what they are supposed to be at instead of 66. I have a Ultra133 card at my friends, but he is using it. grr.

I also wont go with anything other then Windows 2000 Pro/Server. Xp is to slow for me and 98 is a super fast but waaayyy unstable.

^^ That Right there is MY BEAST!!! haha. I had it running good enough to keep up with (unmodified, junked up ) DELL and Gateway 2ghz machines. But now the mobo I have in is acting and slowing my comp right down.

Aight.

So the bus speed for the memory wont change by adding more chips. Aight. So Basicaly only the bandwidth changes? Using 2 PC3200 chips will give you 6400MB/s transfer rate in the end when in dual channel? If so, what if you install 4 chips. Bandwidth doubles right? Just the bus speed stays at 200mhz

The 200 Mhz bus speed is disapointing now since I was reading 2ghz bus speeds. lol. So in slower or faster processors. How am I supposed to know what the bus speed will be? 133, 150,166,183,200,250 etc.. ?

Athlon 64 3200+ @ 2.5Ghz

Above quote is from Flankers computer description.

I though when I saw Athlon 64 3200. that ment the Athlon 64 would be running a 3.2 Ghz! not 2.5ghz!

This will be a very long thread im sure.

thanks for all the help everyone.

Justin -

 

[Flanker]

As for my overclock; the Athlon 64 3200 is a 2.0Ghz processor. The "3200+" means that it is the equivalent (approximately) of a Pentium 4 3.2Ghz processor. I've overclocked it to 2.5Ghz up from 2.0Ghz. It can go higher, but its running too hot for me to raise it any higher without better cooling.

No, not even the bandwidth will double. There is something called "Dual Channel" that most new motherboards have incorporated onto them. If you have 2 identical sticks of RAM running on one motherboard, they will have increased bandwidth but won't double the bandwidth. If you have 2 sticks of 512MB DDR400 memory, it will simply be 1GB of memory running at 200Mhz. The only difference in your system from having more memory will be just that...you will have more memory. Thats not a bad thing at all, but you won't see any other increases.

And the BUS speed of the whole system won't be 200MHz. Thats just the base speed. There is a "LDT" multiplier than multiplies the "200Mhz" by 5 for a total system bus (HyperTransport Bus) speed of 1GHz. Because AMD System Buses are DDR (Double-Data Rate, not only for memory) enabled, this 1GHz bus speed gets doubled to 2GHz. Theres the 2GHz you were looking for :classic:

If you get a AMD Athlon 64 3200+ (2.0Ghz, $200) it will blow away your old system, and will crush those 2.0Ghz Dells and HPs.

AMD microporcessors perform MUCH better than Intel microporcessors because of shorter pipelines and some would argue better instructions. A 2.0GHz AMD can rival a 3.2GHz Pentium 4 in regular tasks, and will beat that 3.2GHz Pentium 4 in games.

 

[viperdude152]

No, not even the bandwidth will double. There is something called "Dual Channel" that most new motherboards have incorporated onto them. If you have 2 identical sticks of RAM running on one motherboard, they will have increased bandwidth but won't double the bandwidth. If you have 2 sticks of 512MB DDR400 memory, it will simply be 1GB of memory running at 200Mhz. The only difference in your system from having more memory will be just that...you will have more memory. Thats not a bad thing at all, but you won't see any other increases.

Ah ok. So now if we are running on a single channel and use 2 sticks of ddr400 512mb you will see 1GB running at the equivilant of one DDR400 stick? With dual channel does it basically see 2 chips as one?

I have been browsing the net for a while now and found some info on the AMD 64 CPUs. The main thing that was confusing me I guess and someone earlier pointed this out to me but I never thought anything of it, is that the memory controller is built into the cpu so the DDR is on its own bus? Instead of on the Hypertransport bus or FSB? I think that was confusing me the most since I was seeing 1ghz bus speeds and couldnt find any ram for it. lol.

There is a "LDT" multiplier than multiplies the "200Mhz" by 5 for a total system bus (HyperTransport Bus) speed of 1GHz.

The LDT multiplier. Is that built into the CPU or the Motherboard? Is that the multiplier the CPU uses to multiply the bus speed to get the 2.0gh+ CPU speeds?

Im Starting to get the whole thing. YAH! Finally once again im moving into the tech field. Although there is still alot to remember and learn.

Thanks Again
Justin

 

[Flanker]

Ah, I see where you're getting confused.

Basically, because the memory controller is integrated onto the CPU chip, the CPU dosn't have to first go to the northbridge and then talk to the memory. The CPU can talk DIRECTLY to the memory, which hugely improves performance.

As for the dual channel. Forget about 1 or 2 or 4 DDR400 sticks for a second. DDR400 simply designates the speed of the memory. DDR stands for "Double Data Rate." It means that 2 instructions will be sent every clock cycle of the memory. This effectively doubles the speed of the memory. If the memory has a speed of 200Mhz, then due to DDR, the speed will be increased to 400Mhz. We don't normally call it 400Mhz, since the core clock speed is still 200Mhz, but we DO call it DDR400.

So you see, the speed of the memory has nothing to do with Dual Channel or anything. Dual Channel simply gives the 2 or 4 memory sticks their own channel to communicate with the CPU and the rest of the system. Dual channel doesn't see 2 sticks as one, it gives each stick its own channel (although I can see why you might think that).

As for the LDT Multiplier; its built into the motherboard. Its different from the CPU multiplier (which is really called the CPU multiplier). The LDT multiplier is a multiplier that the motherboard uses to find the system Bus speed. Keep in mind that there is NO FSB in an AMD System, there is the HyperTransport Bus which connects every system to every other. But because AMD has been able to use DDR (Double Data Rate) with their Bus also, the 1.0Ghz that you get from multipling the LDT Multiplier can be doubled to a total system bus speed of 2.0Ghz. Like so;

200MHz (The internal clock speed) x 5 (LDT Multiplier) = 1.0Ghz x 2 (Double Data Rate, DDR) = 2.0GHz.

The Internal clock speed, or the HTT, is like the FSB on an Intel system. However, it is not a bus, it is simply an internal clock off of which the other parts of the system get their speeds. For example, the CPU;

200MHz (Internal Clock, or HTT) x 10 (CPU Multiplier, varies for other CPUs) = 2.0GHz.

I believe I answered all your questions (And probably created some new ones).

 

[viperdude152]

You have been more then helpfull

my questions are now getting limited. But im sure as days go by I will have others.

LDT. Is it always a multiplier of 5 no mater what mobo you get? Or does it depend on the motherboard? Also. If the multiplier is 5 on a certain mobo, will it stay as 5 or can it be changed?

What does LDT stand for?

thanks a bunch. And yes you answered 99% of my question

Justin

 

[Flanker]

Lol, no problem, happy to help wherever I can.

LDT stands for "Lighting Data Transfer" but thats just a multiplier, I suggest you don't focus as much on that, as the total System Bus speed which is the HyperTransport Speed. No, the LDT multiplier is not fixed, however, it cannot go over its max, which is 5x for most of the newer Athlon 64s. On older systems, like Socket 754 Athlon 64s, the LDT multiplier used to be a max of 4x, resulting in a max HyperTransport speed of 800Mhz (or 1600Mhz with DDR, but that gets confusing sometimes).

The reason you can change the multiplier is because when you're overclocking, you're raising the HTT (system bus) and because of the multiplier, the HyperTransport Bus might go over its rated speed.

So for my overclock: 250Mhz HTT x 5 LDT Multiplier = 1250 HyperTransport Bus. Thats too high, because its only rated for 1000Mhz. (Notice I'm not multiplying by 2, its just a personal preference. Its actually rated for 2000Mhz and the PC would be running at 2500Mhz, which is too high). But if you set the multiplier to 4x, the speed comes out to 1000Mhz, just like its supposed to be.

 

[Apokalipse]

actually, Athlon 64's do have a FSB, but it is inside the CPU itself.

normally, you would have a seperate memory controller on the motherboard (Northbridge), which communicates with RAM, then the CPU would ask the memory controller to send/recieve data from RAM
the FSB is the speed between CPU and memory controller

Athlon 64's have the memory controller on the CPU itself, therefore the FSB is inside the CPU
the memory controller being on the CPU means they communicate directly to RAM.
the speed between CPU and RAM on Athlon 64's is called the HyperTransporT (HTT)

now, the total HyperTransport on Athlon 64's is 2000MHZ (1000 for memory)
each memory stick gets 200MHZ by default (DDR400) but you can increase that as far as the RAM and CPU will run at.

all Athlon 64's have the ability to lower their multiplier, but not raise it (unless it's an FX)
say the CPU had a core speed of 2000MHZ
that would be 200 HTT x 10
if you lower the multiplier to say 8, you can then increase the HTT to 250MHZ, so you can run DDR500 memory at stock, and the core speed still at stock (250 x 8 = 2000MHZ)
although if you kept the multiplier at 10 and raised the HTT to 250, you would get an overclocked CPU at 250 x 10 = 2500MHZ

 

[viperdude152]

Well I got the AMD side pretty well figured out.

How about the intel side? Do you figure it out the same way?

 

[Flanker]

Nope. The memory has to go to the northbridge first, and then talk to the memory, resulting in a much slower transfer.

Also, the system clock of the Intel Systems (The FSB, Front Side Bus) is also the system bus, which complicates and simplifies things at the same time. However, the FSB also runs with a 4x max multiplier.