Jump to content
Sign in to follow this  
Speedpc

Confused by HTT? LDT? FSB? A64??? READ THIS!

Recommended Posts

[quote][i]Originally posted by David Stewart [/i]
[b]Ok. I think I'm getting it now. I have been running at 2.4 Ghz. (240x10) with an HTT of 1920 (fsb240x4=960x2). For experimental purposes I changed the LDT/FSB Ratio in Bios from Auto (4) down to 3. This gave me an HTT of 1440 (fsb240x3=720x2=1440). I was then able to raise my FSB up to 255 stable which gave me a cpu speed of 2.55 Ghz.

So, If I understand correctly 2.55 Ghz with an HTT of 1440 is faster and more efficient than 2.40 Ghz with an HTT of 1920. Makes sense. I wasn't sure until this was explained in detail that the trade off between HTT speed is really not as important as raw CPU speed as long as you fall in the HTT guideline range. Correct?

David [/b][/quote]

100% correct ..!!

It took me some time to realize how it all works also.. HTT doesnt impact performance no where near the way cpu mhz does.. You could prolly lower it to 2 and not see much of a difference in performance ..

Im running 245 now with real tight timings and my LDT @ 3 .. she is just flying and very happy here..hehe..

Share this post


Link to post
Share on other sites
This is some really good info, Perfect Job David !!!!!! :) RGone and Angry_Games are sharing there knowledge. and we all learn something, I guess i won't bring up the bios issue again :) lol Still tweaking

Share this post


Link to post
Share on other sites
The thing is this board does not want a bit more ghz it wants LOADS. I am happy with 255x10 at 2-2-2. .I could buy a mobile and knock 1 or 2 secs off, but. I will wait until pci-E comes in before I change again(prolly about 3 months

Share this post


Link to post
Share on other sites
Yea great job guys..

I wish this was around before I started browsing a zillion forums to learn it.. But you guys made it easy to understand cuz I know it was confusing before I got it.

Share this post


Link to post
Share on other sites
k so lemme get this straight

example:

fsb/cpu*=mhz or 200/10=2000
ddr/ldt=htt or 400/4=1600

but what confuses me is, the fsb/2 = ddr right?
so then wouldnt my ddr266 ram be running at ddr400 by default?

Share this post


Link to post
Share on other sites
[quote][i]Originally posted by reactor [/i]
[b]k so lemme get this straight

example:

fsb/cpu*=mhz or 200/10=2000
ddr/ldt=htt or 400/4=1600

but what confuses me is, the fsb/2 = ddr right?
so then wouldnt my ddr266 ram be running at ddr400 by default? [/b][/quote]

Nearly. Hope this doesn't just confuse you more :P

Total CPU Mhz == HTT*Multiplier
HTL == 2* (HTT*LDT)

Forget about DDR for now. Your ddr266 RAM you mention, that would be 133Mhz which i kinda don't think you're running .. or atleast you shouldn't be in this day and age of overclocking.

DDR == Dual Data Rate, so whatever speed your RAM is set to (HTT 1:1 or on a divider) is the clock speed it'll run at [u]before[/u] doubling.

Again, hope this doesn't confuse you more :shake:

Share this post


Link to post
Share on other sites
reactor

your RAM is actually only 133Mhz...but since it can do 'double' the data rate than SDRAM, it is considered "DDR"....and the 266 you get from DDR266 is simply...133 doubled.

so you have PC3200, which is 200Mhz, doubled is DDR400.

PC4200 is 267Mhz, or doubled is DDR533

LDT (HTT) multiplier is default 4x on your cpu and therefore your board.

so we take your RAM for this example:

133Mhz x2 = DDR266, or 266Mhz.

266x4 (your LDT multi by default) = 1064Mhz, which is your HTT speed.


now...i have not said anything about cpu Mhz or cpu multiplier. Now I will explain that, but make sure you have the above in your mind and understand it (it will be like half a lock clicking open heh...the other half of the lock is below!)

you have an Athlon64 3000+

According to my AMD tables

[url="http://www.angrygames.com/AMD_CPU/AMD_A64/AMD_A64.htm"]http://www.angrygames.com/AMD_CPU/AMD_A64/AMD_A64.htm[/url]

your cpu is 2Ghz. Since these cpu's have a default FSB of 200 (or again, 400Mhz DDR), your cpu multiplier is 10x

10x200Mhz = 2000Mhz

now you say, your RAM is only DDR266...so how does all this work? This is the part where RGone is going to step in in a day or three and do the 'ho-down' on memory ratios for anyone that doesn't know.

I'll just include rudimentary memory ratios and you might catch the drift...

suffice to say, your DDR266 and your 200FSB cpu would be running in a ratio of 2:3.

If you had PC2700, (or 166Mhz doubled, would be DDR333, or 333Mhz), then your ratio would be 4:5

if you had PC3200, (or 200Mhz doubled, would be DDR400, or 400Mhz), then your ratio would be 1:1 (meaning that the RAM and the cpu were 'in synch' with each other.

dont let that all confuse you though lol.

HTT speed is the speed that data can flow over the cpu's 'Hyper Transport Tunnel'. This is like how data could travel from cpu to northbridge in AthlonXP and Pentium4 motherboards.

Difference is, A64 has this 'northbridge' built into the cpu (the memory controller anyway). It doesn't really have anything to do with how fast the cpu's Mhz are. It only has to do with how fast data can flow over this internal link in the cpu between the logicical processor and the memory controller.

now two things...as psy says...hopefully you arent running DDR266...and if you are, save some money and get some DDR400. Trust me on this. You want at least DDR400 or higher, 512MB modules at least (if you can get a gig of RAM then great)

second...hope this didnt confuse you more!

Share this post


Link to post
Share on other sites
Guest Byron
Let me see if I get this straight:

On my stock 64 3400 the FSB at auto is 200x12 for a total of 2400 mhz. 200x2x my HTT (which at auto is 4) is stock at 1600? Is that right?


This seems to be true until I mess with my FSB multiplier. If I only change the FSB to 210x10 and nothing else, Sandra reports 840x2=1680. That would stand correct with 210x2x4=1680.

When I change my settings like this:

224x11.5 and my HTT is still on auto and memort still also on auto then sandra reads my FSB at 2x808(1616 MHZ data rate)

The part I dont understand (and the numbers dont calculate correctly) is the last one with 224X11.5 which gives me 1616 in sandra. Where is the 1616 coming from? I have attached my saved benchmark to look at. Any ideas?

This is sandra 2005 lite BTW, if that makes a difference.

NUMA Support : No
SMP Test : No
Total Test Threads : 1
SMT Test : No
Dynamic MP/MT Load Balance : No
Processor Affinity : P0
Number of Runs : 64000 / 640

Processor
Model : AMD Athlon(tm) 64 Processor 3400+
Speed : 2.58GHz
Model Number : 3400 (estimated)
Performance Rating : PR3864 (estimated)
Type : Standard
L2 On-board Cache : 512kB ECC Synchronous, Write-Back, 16-way set, 64 byte line size

Chipset 1
Model : Nvidia Corp ??? (00E1)
Front Side Bus Speed : 2x 808MHz (1616MHz data rate)

Chipset 2
Model : Advanced Micro Devices (AMD) Athlon 64 / Opteron HyperTransport Technology Configuration
Front Side Bus Speed : 2x 808MHz (1616MHz data rate)

Features
SSE2 Technology : Yes
SSE3 Technology : No
HTT - Hyper-Threading Technology : No

Share this post


Link to post
Share on other sites
Guest Byron
Further testing holds true when I dont mess with anything else (well except for my vcore) and change:

215x12: This in sandra calculates to 860x2=1720, and thats what sandra reports.

When I change it to 215x11.5 it reads 2x808 at 1616.

Maybe I am missing something, and its late so that might be why.

Any explanation would be great. Thanks!

According to what I am understanding the cpu multi doesnt have anything to do with the HTT multi, and if thats true either Sandra is calculating these wrong or I am missing an equation out of this formula.

Thanks again

Share this post


Link to post
Share on other sites
[quote][i]Originally posted by Byron [/i]
[b]Further testing holds true when I dont mess with anything else (well except for my vcore) and change:

215x12: This in sandra calculates to 860x2=1720, and thats what sandra reports.

When I change it to 215x11.5 it reads 2x808 at 1616.

Maybe I am missing something, and its late so that might be why.

Any explanation would be great. Thanks!

According to what I am understanding the cpu multi doesnt have anything to do with the HTT multi, and if thats true either Sandra is calculating these wrong or I am missing an equation out of this formula.

Thanks again [/b][/quote]

The way I understand it the X.5 multis are kind of artificial in that it will instead use the next multi up and drops the memory speed to give the same resulting overall CPU speed. I believe this is an oddity of the NF3 design.

Therefore 215 x 11.5 would equal 206 x 12 or there abouts.

Share this post


Link to post
Share on other sites
alright guys i get it now thanks.

and yes i am running ddr266 :( can only get to about 2200mhz maybe a bit higher but i know 2300 wont go even with loose timings and an upped voltage.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×