CAS vs FSB

brettmar

Obliviot
Ok, here is the situation.

I have some Mushkin Basic memory that I am going to install in my 2nd PC. It is rated cas 2.5 at 400mhz. I also have some PC4000 memory. Both rated at one gig. Now, should I get a better performance increase by bumping up the FSB on the board, giving the boost to the CPU and Memory, and give the CAS latency 3, or should I drop the CAS latency to 2.0 and leave the FSB at 800? I have tested the Mushkin memory, and it will stay stable at 2.0.

The only other option I have is to go with corsair XMS Xpert memory, and do both, but that is big buku bux there.

Cooling is NOT an issue. I have very low temps, and plan on redoing my water cooling next week.

The chip is a P4 3.0 Extreme Edition btw. asus p4c800 Deluxe motherboard.
 

Will Nave

E.M.I.
Hmm... I think I would require you to ship me your rig for testing before I can offer firm advice. :roll:

Pm me here for a shipping address... :wink:
 

Rob Williams

Editor-in-Chief
Staff member
Moderator
I don't know much about Ram timings.. it's something I definately need to study.

However, have you tried playing around with Memory benchmarks? I recommend you try SiSoft Sandra if you haven't before. It has pretty decent Memory benchmarks, and allows you to compare your results to similar other set ups.
 

Nosebiter

Obliviot
Okay here we go and this is going to be a mouthful....

There are two sides of this fence, there are the pure CAS timing folks who equate lower cas times to increased memory performance, and those who believe CAS times are secondary to memory bandwidth by increasing the ram speed. To be honest in certain applications both are correct, so let me explain.

The first side of the coin is the fine tuning, or the "superbike" argument. By finely tuning your ram down to the lowest cas times possible(2 usually) you can ensure that the stobe fires and refreshes as quickly as possible on the ram banks, this will make absolutely certain that there is the least amount of slack during operations. In other words, the ram will function more efficently, much like what a supercharger does to a car engine. This will not increase memory bandwidth much, but it will take what you have and make it perform a hell of alot better then it would otherwise. This gives the illusion of more bandwidth, because more effecient ram, can handle more operations. The reason why low latency ram costs more, is because the faster cas times tax the substrate a lot, and the reason most ram can't handle this is because there is 0 margin for error. When ram is zipping along at cas 2 it's alot like racing down the road at 150mph, you can't make a single mistake. The reason why low latency ram doesn't traditionally overclock well is because of heat and signal noise. Super fast cas runs hot, and makes a crapload of signal noise, and even a single error along the strobe will cause a dump in the entire cycle and you will lose everyhing currently riding over that ram bank, ie it crashes. So keeping memory in parameters becomes essential. This style of fine tuning benefits quick small changes, like those commonly found in video games or the like. This is akin to a nimble machine, that stops on a dime and start up again just as fast.

The other side of the coin is pure bandwidth, or the "harley davidson" argument. By giving the CAS times some slack you are not asking as much of the ram in reguards to heat and signal noise, so you can punish it alot more before it cries uncle. By relaxing the CAS times, you can ramp up the memory clock signifigantly, because the extra heat and signal noise created by such a massive overclock, is tolerated by the ram simply because it doesn't have to pass the data around internally as fast. Much like a harley, they pour on the horsepower with minor performance upgrades and hope the extra horsepower makes up for the ineficiency of the engine itself. The same theory applies here. If you jack up the ram clock you increase the memory bandwidth available to the process with the hope that the processor will be swimming in memory and not need to pre/re-fetch as often. This stile of fine tuning is more suited to extended taks, such as editing, or content creation. Think of a steam shovel moving massive amounts of earth per movemnt, slow on the uptake and reload, but it can move a cubic assload of material in one motion.

I myself have found that to squeeze the most performance out of your ram, you need to find a happy medium between these two styles of memory tuning. Lower your CAS as far as it can go, and then try and overclock it, keep going till it becomes unstable. Once you hit that point back off and repeat the process until you hit the stability you are searching for. I've discovered on a good stick of Corsair or Mushkin I can keep cas2 and hit 240-250mhz on the ram, which is pretty god damned good. With such a high overclock running at cas2 my memory timings are off the charts. Also remember with lowered CAS times your can overclock your processor faster as well and keep the memory in line with that, so that is also something to take into account. Hope this helps, if you have any questions launch away.
 

brettmar

Obliviot
Thank you for your help. I agree with you on the CAS latency. I prefer the access strobe to be at it's lowest before it hits the next row. The issue I am considering though, is the value of the BH-6 chips that I plan on using. On a dual channel setup, I am already getting very good performance, using my current setup. Being a [H]ardcore (sorry for the plug on another site) computer geek, I have to update at least once a month or two. I can afford to do so, so no worries. I still do not like the idea of overpaying for something that will not provide a great benefit to me though.

Basically, to narrow down my question, which will help render video and still images faster? Corsair 2225 rated memory, or eased latency, high FSB?
 

Nosebiter

Obliviot
No worries I got [H] Love. I'd go with the fast CAS time ram, and see how far it overclocks, and whatever clock it's stable at, then keep it there. I'm not a fan of jacking up the FSB with slow CAS times, unless I am running a server environment.
 

Rob Williams

Editor-in-Chief
Staff member
Moderator
Kudos to [H].. they are one of the reasons I love hardware so much.

Thanks for the great explanation Nosebiter! I think I will play around with my timings sometime this afternoon. You seem to know a lot about this type of stuff.. right on. Don't be surprised if I ask for help sometime later on :p
 

Nosebiter

Obliviot
Heh, all this Mem timing makes me want to go home and see how much more performance I can squeeze from my trusty Corsair. I truly push my hardware to it's limits in the name of performance.

Np Rob. My geekery is freely shared. :D
 

Rob Williams

Editor-in-Chief
Staff member
Moderator
Hopefully you do a better job than I do.

I blew up three PSU's and one video card in the past. Hope that's all going to stay behind me ;)
 

Word.

E.M.I.
Yea. Killing stuff does suck but it happens alot!

Just Want to say Nice topic i read the Posts and replays and learned some stuff for myself. i know some what about all the RAM stuff I am curretly in Tech school Rob. if u want i can lend you my big ass book of BS lol it Explains all the stuff abit. Drop me a line .. Also if anyone wants i can Type the info it says if you really want lol.
 

Rob Williams

Editor-in-Chief
Staff member
Moderator
Yeah, I wouldn't mind taking a look at that book, could be interesting. Aren't you supposed to be learning from it though? :shock:
 

brettmar

Obliviot
LoL...tech school grad here too.

If you need books, maybe I can get an all access pass for the site to my books24/7 online thing. It is real nice. Every PC topic known, thousands of books, free. Let me see what I can do.
 

brettmar

Obliviot
Ok. I went ahead on getting 4GB of Corsair XMS PC3200. 2 of these are the XMS Xpert line, the other 2 are just XMS TwinX. All 4 are rated at 2.2.2.5, and they are digital LIGHTNING!
 

dukeman

Obliviot
wow, 4 gig is overkill for just about everything but heavy cad.

just my 2 cents but you should of gotten all the same exact type of memory. even though they are close there still might be some compatability issuses.

not to push another website buy http://www.extremeoverclocking.com/ has a pretty good forum that has just about every question you could ever think of about memory. Some of those guys know alot about the old tight timings vs high FSB fight.

if that memory doesnt work for you just send it to me and i will test it for you.
 
Top