Well, I'm not sure if my concept on HTT is correct. From what i know, not all the review sites gave the same concept about the HTT on Athlon64 system. Some said the HTT has something to do with memory and some said no. Even the DFI-street mentioned this : " Basically HTT is your memory controller's communication speed". However, I found out from AMD datasheet that HTT is not related to memory controller at all, as they are 2 independent units.

So I would really appreciate yr opinions and thoughts regarding HTT.


Some simple rules in discussion:

1. When you post any facts, state the source. (links or screenshots)
2. NO bashing or flaming.
3. You can make comparison of HTT with FSB.
4. No discussion that is not related to topic.
5. Pls stick to HTT on K8 system only.
6. Technical discussion is welcomed.

This post has been edited by charge-n-go: Oct 30 2005, 11:50 PM

EXPERIMENT DONE, THANX TO ALL WHO CONTRIBUTED

Now, it's experiment time. We'll try to test if HTT clock has any effect on performance, when CPU and RAM are kept at stock speed.

Please contribute screenshots with the following settings :

TEST 1

1. CPU and RAM are set to 1800MHz, DDR400 respectively with different HTT values.

2. The settings are :
--> 9.0 x 200 (CPU: 1800MHz, RAM 1:1 @ DDR400)
--> 7.5 x 240 (CPU: 1800MHz, RAM 6:5 @ DDR400)
--> 6.0 x 300 (CPU: 1800MHz, RAM 3:2 @ DDR400)
--> 4.5 x 400 (CPU: 1800MHz, RAM 2:1 @ DDR400)




TEST 2 (ikanayam's suggestion )

1. CPU, RAM and base HTT speed are set to 1800MHz, DDR400 and 200MHz.

2. The settings are :
--> 9.0 x 200 (HTT multiplier = 3.0x)
--> 9.0 x 200 (HTT multiplier = 4.0x)
--> 9.0 x 200 (HTT multiplier = 5.0x)
--> 9.0 x 200 (HTT multiplier = 6.0x)


*Sandra CPU, Sandra Memory and SuperPI result is compulsory

*CPUz (CPU n RAM) reading is compulsory.

* 400MHz HTT base is not necessary if your board cant do it



This post has been edited by charge-n-go: Oct 30 2005, 11:49 PM

well, from what i know is that HTT is a bus that connect the processor to the other hardware on motherboard. HTT is FSB replacement.

well, i think memory unit is another thing from HTT cuz from wat i read from AMD website, HTT have 8.0GBps effective bandwith while processor-to-memory have independent 6.4GBps bandwith which makes total effective 14.4GBps.

While HTT is generally a high speed bus developed by Hyper Transport Consortium, i think you might find more info regarding HTT on the hyper Transport Consortium website.

HTT is not owned by AMD alone, it's developed by the HT consortium SIG by quite a number of manufacturer.

Memory unit is confirmed not another thing from HTT. See the screenshot in post #2. It's from AMD Athlon64 datasheet. Pls give the link for the facts u claimed. Thx

The current HTT discussion is only on AMD system, coz it will benefit most of the forumers who are PC users.



Yes, it is true. One thing to add: HTT is not an enhancement of FSB system. From official HTT website, i found some facts:

HyperTransport chip-to-chip interconnect technology is a highly optimized, high performance and low latency board-level architecture for embedded and open- architecture systems. It provides up to 22.4 Gigabyte/second aggregate CPU to I/O or CPU to CPU bandwidth in a highly efficient chip-to-chip technology that replaces existing complex multi-level buses.

* the Northbridge and Southbridge system tat uses FSB is a complex multilevel bus system.

Source

This post has been edited by charge-n-go: Sep 20 2005, 03:27 AM

Temporarily moved to OC United to gain more feedback. I'll move it back to H/w once you get enough info and opinions

I think this is more of a hardware discussion than it is an OC discussion.

Anyway an easy way to test if memory bandwith is directly tied to HTT bandwith to decrease the HTT LTD multiplier to 1x and see if the dual channel memory bandwith decreases accordingly.

From everything gathered so far i think it's quite clear that HTT is only for I/O other than RAM access. That's what the onboard RAM controller is for in the 1st place.

from the way ikanayam describe it it seems that HTT is the 'other route' or connection towards I/O and not to the memory unit itself? My question is when the HTT is raised how does it effects the memory controller itself to give more grunt...Undoubtably is the Memory Controller doesnt reacts to the HTT it seems that it is on its own no matter how fast we clocked it via HTT...am i right or wrong here???The only thing that matters is the muttiplier itself which is the source key which depends on how fast should the processor runs and also determined the processing speed.

If HTT is no way connected to the CPU (FSB theory) then raising the HTT will increase the speed of transfer rate between I/O to the CPU and not to the ram??Then how come the ram connect to retrieve data and process it simultaneously???

This is wat i get from AMD spec sheet and i cut and paste the PLL table in another page to merge with the block diagram.

The HTT clock_out pin isnt connected to MEM_clock_in pin at all. PLL is known as the clock generator inside the CPU, and it provides reference clock for other parts in CPU. CPU core cloc, HTT clock and memory controller (not RAM) is derived from PLL clock with multiplier. Let's say an Athlon64 3200+ running at 2.0GHz co and 2.0GHz HTT.

1. The base clock for PLL is 200MHz, CPU has a multiplier of 10x and HTT has a multiplier of 5x. HTT = 2000MHz because it's a single 16-bit link config rather than 2x 8-bit HTT links.

2. Memory controller is running at the same clock as CPU (2000MHz). The RAM is clocked in reference with memory controller. That's y in CPU-z u see the divider as CPU/10x for a DDR400 RAM, if you hv an Athlon64 3200+.

3. The so called 'HTT' overclocking in motherboard is actually raising the PLL clock. Hence increasing PLL affects the HTT, CPU and RAM speed.

4. Since HTT bus can't take very high clock, when u set the PLL to 250MHz, it's better to decrease the HTT multiplier to 4x so that it remains 1000MHz per HTT link (effectively 2000MHz for 16-bit).

5. Basically setting the RAM to DDR400 and increase the PLL (or HTT in mobo BIOS) has nothing to do in increasing the bandwidth between RAM to CPU. I've said before overclocking the PLL (HTT) with all the other parts like CPU, HTT and RAM remains at stock speed doesnt bring any good,and not an overclocking. For example, if you able to push PLL up to 400MHz, but the HTT multiplier is set to 2.5x, CPU is set to 5x, everything is running at stock and it's useless coz no performance boost.

6. the memory databus is indicated as MEM_DATA [63:0] from the printscreen attached. It's a 64-bit bus which means a single channel memory interface. Dual channel will have MEM_DATA [127:0] pins. This clearly states the data from memory doesnt go through HTT, and the RAM is directly connected to CPU memory controller with another dedicated bus.



more on memory controller divider can be found in Anandtech

more on HTT used in Athlon64 platform can be found in Xbitlabs

Quote from Xbitlabs (Opteron which has three 16-bit HTT links):



This post has been edited by charge-n-go: Sep 20 2005, 10:47 AM

Aiks... I need some hardware expert in hardware section to comment it technically.


It's because I kinda confused by mobo manufacturer as they put the term HTT as PLL, so i wanna double confirm how the HTT actually works. From the info gathered so far, i didnt see any relation and this might prove 2 things :

1. The mobo manufacturers have different concept on HTT.

2. The mobo manufacturers don't wanna confuse the overclockers since we are so used to FSB. Thus making HTT like a FSB will be easier for overclockers to play the settings.

Well, if we overclock a system, we dun need to understand the operation of HTT. As long as we see performance boost, it's good enough. However, freak like me wanted to know how the HTT works so that I know which settings can be optimized during overclocking

This post has been edited by charge-n-go: Sep 20 2005, 05:18 PM

My goal here is to increase the understanding of the true nature HTT technically as well as the effects that it has on OC'ed systems. However this is just a trial to see what can we gain by sharing this between the OC guys and the techy guys. It's not a big deal if I move it back to H/w but was thinking that maybe it maybe dispel more myth about HTT since someone did say the termination over at DFi-Street was flawed and should be corrected

Can u pls make a link to hardware section as well? Some techies might not enter O/C united forum. I need them to correct me if anything goes wrong bcoz i m not 100% sure about my assumption. Of course i dun want ppl here be misinformed by my assumptions.

Thx.


* edit : I've put a link in AMD vs Intel to this thread.

This post has been edited by charge-n-go: Sep 20 2005, 05:33 PM

Figure 1: HyperTransport technology introduces a new bus architecture that offers higher
performance and greater flexibility; its packetized approach also simplifies system
hardware design. Source: AMD By: devx.com



Figure 2: HyperTransport technology can provide a streamlined interconnect for SMP
systems, reducing bottlenecks between processors, memory hubs, and memory
DRAMs. Source: AMD By: devx.com

main source : http://www.devx.com/amd/Article/17437

Evogenix

This post has been edited by Evogenix: Sep 20 2005, 06:59 PM

I agree. Someone with higher CPU clockspeed but with a same RAM speed as others has higher memory bandwidth. The CPU clockspeed plays an important role in OCing an AMD64 system.

Please refer to dinster's Sandra Memory Bandwidth thread.
http://forum.lowyat.net/index.php?showtopic=154304&st=0

Here is an article about HTT from wikipedia.
http://en.wikipedia.org/wiki/Hypertransport

Actually my AthlonXP system scores better in Sandra too, if the CPU clock speed is increased. At 2.0GHz DDR510, the score is around 150MB/s less than 2.4GHz. I guess it's due to the faster memory request from CPU to RAM (in AXP case).

In Athlon64, memory bandwidth won't increase as CPU clock increased (if the divider is set correctly to limit the RAM at DDR400). However, the latency to access the mem controller should be faster, bcoz latency = 1/ clockspeed.

FYI, Athlon64's mem divider is a bit weird. Let's say u hv a weird CPU clock (eg. 2222MHz), the RAM clock might not reach DDR400 (200MHz) but around 193MHz only. Here's the scenario :

at 2200MHz, RAM works at 200MHz (DDR400) when divider is set to 11x.
at 2222MHz, RAM works at 202MHz (DDR404) with the same divider as 2200MHz, but AMD doesnt allow the RAM to work higher than specified bcoz it might caused instability. Hence, it will lower the RAM speed with a higher divider, maybe 11.5x, so that the RAM works at 2222MHz / 11.5 = 193.22MHz.

Well, I'm not sure how many sets of divider supported. Hope somebody can find and post here

* if not mistaken, the memory divider settings article is from Aceshardware. I cant find it though, need to search back when I have time

It does increase in sandra memory bandwidth test. Read dinster's thread AMD64 section.

tampoi scored higher than mine because his clockspeed is higher than mine. Can you explain this?

lol, i oso dunno the exact cause ler.

Memory bandwidth = memory speed x data width. Eg. DDR 400 dual channel has 400MHz x 128-bit = 51200Mbit/s = 6.4GB/s. If your RAM remains at DDR400 while scaling up the CPU, the memory bandwidth is fixed.

Yeah, the score is higher, no doubt bout it. Even my AthlonXP can do it ler. I got 3757 @ 8.0 x 255MHz and 3900 @ 9.5x255MHz. As mentioned b4, i suspect it's due to the faster mem request from CPU to RAM. I might be wrong though. Siapa mau betulkan saya?

not really, it's because his timings were superior more like it.

Eh? Do I have anything to do with the starting of this thread?



You're probably right in the sense that HTT only concerns I/O.




BUT...



So.. this is the technical verdict lar. Everyone's intepretation of HTT can be different I guess.

This post has been edited by skyther: Sep 20 2005, 10:30 PM

yo skyther, not bcoz of u la
I'm receiving msg regarding HTT actually, and many seemed confused with HTT even myself

It's good to have an open discussion. But then this time we limit to A64 system only bcoz most of us here are PC users.

btw, can u give us the link to your quotes? thanx

This post has been edited by charge-n-go: Sep 20 2005, 10:35 PM

^

All from hypertransport.org lar...
http://www.hypertransport.org/applications/apps_PCs.cfm
http://www.hypertransport.org/consortium/cons_faqs.cfm << this one's pretty good



Come to think of it, Intel seems to be ignoring the whole thing. I wonder if they're going to come up their own version of a bus revamp for their next gen processors.