General note to all: This will eventually be turned into a guide, or linked, for PC system reference, after thinking about it for a few more days, to help people figure out what to do for the Christmas PC. Yeah, its long and technical... but actually not too deep. Do not assume you are an expert & jump into making BIOS changed in hopes of turning a 2200MHz machine into a 9000MHz machine. It won't work that way, and you might hurt your hardware.

RAM & the PC....

A note about RAM. DDR is runs at 100Mhz (10.0ns access time), 133Mhz (7.5ns), 166Mhz(6.0ns), 200MHz(5.0ns), 217MHz (or more). Unlike older SDRAM, DDR can transfer memory on both the rise and the fall of a clock cycle. So, essentially, you are getting 200Mhz, 266Mhz, 333Mhz, 400MHz, or 433MHz respectively. Peak bandwidth for 200Mhz is 1.6GB/sec and 266Mhz is 2.1GB/sec. The most common, operating at 200MHz, will peak at 3.2 GB/sec. DDR is known as PC1600 (200Mhz), PC2100 (266Mhz), PC2700 (333Mhz), PC3200(400MHz), PC3500(417MHz), etc. (follow the patter to the nth degree), since it correlates to the peak bandwidth potential.

Another thing can be done to improve bandwidth: dual memory controllers. Two separate controllers, each operating in a very delicately balanced harmony at PC3200 (400MHz). This 'balance' is due to electrical characteristics of the individual chip... with dual controllers, you are well adviced to buy matched (& tested) RAM, not grab any old RAM and put them together... it likely will not run stable, if at all (with dual controller enabled). Of course, the advantage here is speed... 6.4 GB/sec, all for the low price of PC3200 RAM.

BTW, companies don't just throw two sticks of RAM together to produce these kits. Testing or qualifying Dual Channel memory might involve something as simple as a QA technician booting up a pair of RAM in a Dual Channel motherboard and ensuring they work together under a set of conditions, or it could be more complicated, including so called "SPD" optimisations and even chip selection. Personally, I use Kingston HyperX. But Corsair is good too (so I hear).

RAM controllers can also be made for brute force, e.g., just run at a higher clock speed. Then you need RAM that will work with the electrical characteristics, and this is what you are paying top dollar for in 533MHz RAM, for instance. I personally prefer dual controllers, and my machine effectively runs about 200MHz faster as a result.

Now for the very technical issue of the numbers. First off, (I hate to be trite), but if you are needing to ask what they are, you should not be pushing RAM settings BIOS. Just put the stick of RAM in the machine, and DO NOT change anything to anything other that "conservative' or 'basic' or 'least aggressive' or 'default' in BIOS. This means do not tweak the RAM. At best you will achive probably 7 to 14% improvement in speed in certain applications (not apps in general, which will see maybe 3% improvement).

All RAM modules have latency settings that control how long the chipset must wait to put data into or get data out of memory. The dominate factor in RAM speed, after clock speed, is something called CAS Latency. It is often mentiond as CL=2 or CL=2.5 or CL=3. CL stands for CAS (Column Access Strobe) Latency, which is the amount of time (in clock cycles) that it takes to retrieve data from the RAM module. CL2, CL2.5, and CL3 refer to the number of clock cycles that it takes before the initial stream of data is sent. CL2 modules wait two clock cycles before sending data. CL3 modules wait three clock cycles before sending data. As you might expect, CL2 modules are faster since they only wait two clock cycles and therefore are usually more expensive.

In a fictional example in standard SPD timing notation, 2-3-4-5-1T means:
2 - CAS Latency (timing latency)
3 - tRCD (RAS to CAS delay)
4 - tRP (RAS Precharge delay)
5 - tRAS (minimum Active to Precharge Delay)
1T - Command Rate (usually 1 or 2 clock cycles)

I started to explain the others, but realized its not meaningful. It will not help, and overriding SPD settings in your BIOS should likely not be attempted by anyone reading this. Let's just say that the most important is CAS Latency, and the lower the better. But at faster RAM speeds, it is unavoidable that CAS Latency must increase. On my home desktop, I run a dual controller CL2 (nForce2 northbridge with 333MHz Kingston HyperX matched), and it is significantly faster (about 10%) in Adobe InDesign or Photoshop than a stock Dell Intel machine running almost identically configured machine at single controller CL3. This performance gain does not apply across the board, to things like daily web surfing, MSN, Word, etc. The gain is probably only 3 to 5% in RTW.

But taking some examples, one particular Corsair module is programmed for 4-5-5-12 operation at 333MHz (DDR667). In another example, Kingston KHX5400D2k2/1G, at 200MHz, are programmed for 3-3-3-9 timings at 200MHz (DDR400), 4-4-4-12 at 266MHz (DDR533), or 5-4-4-12 at 266MHz (DDR533). These are standard clocking and timings. And if the question begins to arise, can you overclock RAM like a CPU, the answer is YES... but extreme care is necessary. Basically, almost nobody should. No one who is needing to read what I am writing to usderstand RAM should attempt it... the risk is to destroy very expensive hardware.

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Hopefully by now, you have an idea about this. Except for one thing. The AMD has a bus frequency of 200MHz, and with the data transfer also added to the rising and falling edges of the clock signal (the squiggley line on an oscilloscope), this effectively doubles the data transfer rate. Oh gee. What to name this innovative process... Hmm.. Double Data Rate (DDR!). So the answer is that the RAM you talked about is wasted money, and in fact it is wasted performance, since it (likely) is slower in certain circuit details in order to allow operation at that speed. In other words, don't buy the RAM with the 'biggest number'.... instead:

MATCH THE RAM CAREFULLY WITH THE MOTHERBOARD and intended system clock settings (its RAM controller, e.g., nVidia nForce2, e.g.)... see the MB maker's manual or website for their recommended RAM and associated most stable timing and latency settings (normally, you do NOT set them yourself... the SPD, or Serial Presence Device, does it for you).

Take this a basically a rule: DO NOT OVERCLOCK RAM.

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It is actually much more complicated that I've described it. When you know how it really works, you will appreciate every nanosecond of proper operation of a modern PC!

RECOMMENDATION: Average gamers should not pour money into 'faster' RAM... the money ($200 to $500 in some systems) is more effectively spend on a better video card, or faster CPU, or better motherboard! If you have a dual controller, then ALWAYS buy a matched pair (kingston or corsair, IMHO) and run the dual controllers! Many people can, but don't (or don't even know they can)!

The RAM you buy is entirely dependent on the motherboard and the BIOS settings of system speed that you intend to run... so match the RAM for the need. It is not possible to give a set answer to "Which RAM should I buy", like it is for a CPU. But if the MB, CPU, and intent of PC use were known, then the RAM type can be determined... primarily based on the MB maker's manual/website, and sometimes 'tweaked' if someone really knows what they want in specific performance applications (and has some good money to get a few measly percent increase in speed in limited applications).

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If by "matched and tested" you mean a Dual Channel kit, I'd beg to differ on that point. As long as the RAM stick has the same product number as the other one, both will run DC fine. I find DC kits to be more expensive than two separate sticks of the same model.

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Totally agreed there. CL2.5 would be just nice for mainstream AMD users. However, I feel that your statement on that Mushkin stick is a little too... extreme. I wouldn't say that it's a waste of money. It's just that mainstream users won't have any use for it.

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No, though that is indeed often true. However, it is less of an issue in more recent systems, and less of an issue in overclocked systems of course. Even RAM off the same assembly line cannot necessarily be matched with certainty. The only way to be sure is to take two sticks of RAM, and run tests on them. To be sure, it is definitely possible, and in recent months even probable to find RAM that is not matched but will work without a hitch. I've even seen RAM from different makers sometimes run together. If you have a local dealer that will test a couple sticks for you out of his OEM RAM bin, or guarantee you can swap RAM (most local dealers I know will in fact do this), then a user can make the match him/her self.

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Quite true. The RAM kit does cost more than 2 sticks, same model number. The small $ extra or so for matched is a tiny price to pay for not chasing down RAM-related problems on a machine. Those can be very difficult to diagnose, and take lots of time to chase. And add the cost of matched RAM only a small bit more, and you have the HyperX which runs rock solid on a wide range of machines and in a large environmental envelope. Heat can be a high-frequency RAM killer/instability source. The Corsairs also have a good reputation (and heat spreaders), as do some others which I am not familiar with (I think OCX?). But I personally know people using Corsairs, and they are rock solid, so I put them with the Kingstons, in my experience.

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Presumably a 4400 costs more than a 3200, and assuming no overclocking, the straight talk is that its a waste of money, since the benefit being paid for is not going to be used. Why pay extra for a 4400 rated module when the less expensive 3200 will do, all things being equal? It pretty much goes with my earlier agreement with you on not buying CL2 RAM, especially on faster machines and larger RAM capacities... but at least in that latter case, CL2 RAM might deliver from 0.5% to maybe 6% performance benefit in certain applications. But 4400 RAM does nothing extra for that money, in a 3200 max system.

Thanks, Although the 2-3-4-5-1T stuff is alot to take in.

I think I understand the CAS Latency stuff now. CL2 is the fastest, CL3 is the slowest.

Can you have Dual Channel 533MHz RAM?

Its a lot to take in, yes. But its not necessary to know all of it, either. But its there for a start

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CL2 is fastest, CL2.5 is slower, CL3 is evenslower, CL 4 is slower, CL5 is slower, and CL6 pretty much drags up the rear. It is NOT linear, e.g., CL4 is NOT 'twice as worse' as CL2. It is fractional, and depends on the application's memory usage pattern.

Higher latencies happen due to many factors, like:
1. Amount of RAM
2. Type of RAM
3. Construction of RAM
4. MB northbridge
5. Lots and lots more.

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Yes. But is must be supported by the motherboard chipset and BIOS (and most will not). In fact, you can overclock the system bus to 533/2=267MHz, and an nVidia 2 dual controller could, in theory, run at 533. That example likely will not overclock successfully that high, however.

Or if you mean DDR2-533, then at the moment, only boards for Intel processors support these RAM modules. AMD won't support DDR2 until next year when they come out with new processors with the M2 socket.

What are these Bridges I keep hearing about.. North bridge etc

I see Syntex is banned, but the questions he asked are still of use to others, so:

The Northbridge is the portion of a computer chipset that connects between the CPU and the major interfaces on the computer including memory, AGP port and PCI bus. It is also connected to the southbridge.

In many ways, these two chips are really the big gorilla in your machine. If they do not just operate, but operate well, and that explicitly means good, high-quality drivers (its almost an oxymoron to say those words "high quality driver" together) which affect northbridge components.

In integrated IGP (integrated graphics chipsets, like nVidia2 MX400IGP), the video controller is in the northbridge chipset. The northbridge chipset can get very hot, and without an excellent cooler, your $3,000 system can be a nightmare of CTDs, BSODs, random lockups, etc. Many northbridges now have active cooling (a tiny, loud, obnoxious, short-life fan) on an inadequate heatsink.

I strongly recommend a 3rd party heatsink for those few who are adept at hardware (most people are NOT adept)... I use the Zahlman northbridge coolers on machines I modify. Many people have northbridge fans that get clogged with dust, or fail, even a few months new. Then they begin getting intermittant BSODs and CTDs and reboots and lockups at seemingly random times. In almost every example, the owner said "my machine is fine, because ... (insert some limp excuse here)". And then we opened the case, and the fan was clogged, heatsink filthy, or fan stopped. Fix cooling, and ohmygosh... no more problems. Look at your northbridge (consult manual, but it is close to the CPU on the motherboard... and on the best CPUs, it is actually inside the CPU).

The southbridge runs much cooler, and is rarely a problem, and rarely needs even a heatsink to dissipate heat.

I heard that Athlon64 processors don't need the NorthBridge, and so A64 boards don't have them. Is that true?...

Mmm... So Syntex is our old friend Callisto. Didn't catch you this time round fella.

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Yes. In fact, some new Intel boards don't have it either.

Northbridge is a chipset that communicates with the computer processor. Northbridge communicates with the processor using the frontside bus (FSB). Northbridge is one part of a two-part chipset called Northbridge/Southbridge. Southbridge handles the input/output (I/O) functions of the chipset. The NB controls interactions with:
- System memory
- the PCI (Peripheral Component Interconnect) bus
- Level 2 cache
- all Accelerated Graphics Port (AGP) activities.

As a note, the Intel Hub Architecture (IHA) is replacing (used in Intel's 800 series chipsets) Intel's own Northbridge/Southbridge chipsets. The IHA chipset also has two parts: the Graphics and AGP Memory Controller Hub (GMCH) and the I/O Controller Hub (ICH).

Starting with AMD's Venice, the bus runs at 2000MHz, and that's partly how they get 14.4 GB/sec CPU-system bandwidth. The fully integrated DDR memory controller can hit 6.4GB/s with PC3200 DDR SDRAM, and helps speed access to memory by directly connecting the CPU to the main RAM.

However, the classic 'Northbridge' is 'gone' from the MB, but the Southbridge is still there: its the nForce4, which is the silver square with the black fan in it at the bottom center of the picture, between & below the SLI card slots, and to the left of the 4 RAM slots. The southbridge does run warm on new high-powered nVidia nForce 4 SLI boards.

Here's the ASUS A8N-SLI Deluxe:

[This message has been edited by Wartrain (edited 12-14-2005 @ 01:30 AM).]

I see. Thanks for the info dude.

Anyway, when I saw the Asus A8N32-SLI Deluxe (can see a pic of it here, btw), I see a metal block below the CPU socket. I assume that's not a Northbridge, just part of the heatpipe?