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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an AMD Athlon 64 has a max speed of PC3200, so If I get Mushkin Extreme Performence XP4400, that won't work?
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.Quote:
Whats all this 2-3-3-5 stuff? I keep seeing it, 2-3-4-5 or some numbers. What the heck are they? Looks complicated...
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).