Memory,Bandwidth,vs.,Latency,T computer Memory Bandwidth vs. Latency Timings

Gone are those times when the companies and the organisations didn't need a hi-tech system to handle them. Owing to the considerable increase in the business sector and thus, an enormous increase in the complexity of the organisational struc ----------------------------------------------------------Permission is granted for the below article to forward,reprint, distribute, use for ezine, newsletter, website,offer as free bonus or part of a product for sale as longas no changes a

Memory Bandwidth vs. Latency Timings All memory is not created equal, nowadays you need to know which 'flavor' isbest for an Intel or AMD PC if you expect the best performance back from yourinvestment. When Intel released the i865PE/i875P dual channel core logic alongside the IntelPentium 4C processors, the memory game changed forever. With a DDR memorycontroller now capable of running dual channel, the Pentium 4 was no longer tobe bandwidth limited as it had been with the i845 series. Those single channelDDR chipsets, like the i845PE for instance, could only provide half the bandwidth required by the Pentium 4 processor due to its single channel memorycontroller.As the new 800 MHz FSB Pentium 4 processors allowed users to hit never beforeseen highs in terms of bus speed, many memory manufacturers were trying tocapitalize on the situation by releasing every increasing degrees of "highspeed" memory.Unfortunately, to run the memory frequency at the same speed as the FSB (or a1:1 ratio) almost all the high speed DIMMs (Dual Inline Memory Module) have tohave very lax timings. Often, these times are as low as 3-4-4-8!Think about it this way, a car built for drag racing can go dead straight superfast, but cannot maneuver as well as an F1 race car. Likewise, the F1 racer isgood in the corners but will be left in the dust on the drag strip. In otherwords, today's high speed memory modules are built for one thing only, and that's top speed, where timings really aren't considered all that much.Memory timings play a key role in terms of overall system performance. More soin 3D based applications which do not need a great deal of bandwidth, butrather quick access between the various pieces of hardware within the computer.Confused about memory timings?When one talks about memory timings they're basically talking about how longthe system has to wait for the memory to be in a ready state before data isfetched or delivered. You could think about memory timings as people working at a drive throughrestaurant; you place your order then wait for the food to be ready. The lowerthe timings are, the faster the computer (and quicker your order comes) isable to get data from the memory, and the faster the rest of the PC willultimately be. This rule of thumb applies whether you're on an Intel or AMD based system. Asfor why there aren't lower timings then 2-2-2-5, JEDEC (the memory governingbody) does not think it's possible for current dynamic memory technology torun at 0 or 1.When we refer to timings it is common to quote a four digit number separatedby dashes (ie. 2-2-2-5). The first number always represents CAS (ColumnAddress Strobe) Latency as it's usually the most important.Next in line is RAS-to-CAS Delay (Row Address Strobe), RAS Precharge andAct-to-Precharge Delay (which is always the final, and largest number).CAS latency is the delay between the registration of a read command and theavailability of the first piece of output data. CAS latency is measured inclock cycles. With all things equal, a stick of DDR memory capable of running 2-2-2-5 willmake the computer operating experience seem faster than a DIMM which may onlyrun at 3-4-4-8. This is because the delay from when the memory receives aninstruction, retrieves the data, and sends it back out is less.Where it starts to get confusing is when you has the choice of buying highspeed memory with slow timings. Just about every PC3700+ rated memory modulewe've seen uses conservative timings after all. If your answer would be tobuy fast memory with tight timings, I'm afraid you're going to bedisappointed as there are no such modules available yet. So, why are we stillinterested in fast memory with slow timings then? Well, the answer goessomething like this....Why release fast memory with slow timings? In highly competitive markets, once a major manufacturer releases a new andinnovative product, the rest will surely follow close behind. If onemanufacturer doesn't follow suit, their products are considered 'old tech'.As always, everything always boils down to money and that's why we have thisdilemma; to run faster memory with slower access times, or run slower memorywith faster access times. There are two trains of thought on this, the first is that high speed DIMMs(like PC4000 DDR) can make up for running slower timings by the amount ofbandwidth provided to the processor. Specifically, bandwidth is the amount ofdata that can be moved from one given device to another.Most DIMMs that run tight timings, such as certain PC3200 & PC3500 modules,have to run the memory at lower MHz than the FSB. However, when overclocking toextreme speeds these DIMMs are bandwidth limiting the processor. What I mean bythis, is that when the processor requires a great deal of bandwidth, the CPUwill have to wait for another clock cycle before being filled, as the memory isjust not fast enough to keep up at the same pace. Having a large pool ofbandwidth is great when you're working with applications that process a lot ofraw data, such as Photoshop or databases for example.The other point of view is that CAS2-rated PC3200 & 3500 memory can make up forthe lack of bandwidth because the memory has a lower latency that in effectmoves data between the CPU and memory faster. Programs that do not require alarge amount of bandwidth tend to benefit more from quicker data transfersbetween the memory and the rest of the computer such as games or 3Dapplications.2-3% Improvement While bandwidth is still very important to the Intel Pentium 4, it's not asimportant as it once was in the i845PE days of single channel memory controllers. Thanks to the i865PE/i875P's dual channel memory controller thingsare much brighter. On average, the system with the memory running at 400 MHz(5:4 memory divider enabled) with aggressive memory timings performed 2-3%faster than the system using high speed memory with loose timings.While that may not seem like a lot to most people, it can make a world of adifference to the enthusiast, especially if you're gunning for that high scorein a clan match where every FPS counts.It seems as if all the large memory manufacturers/suppliers are afraid to loseface by not pumping out high speed memory modules with lax memory timings justso they can list them in their product lines. Many enthusiasts I know, tend tofavor slower memory which allows them to run aggressive timings however.One might say that the benchmarks we used were stacked against memory that usesconservative timings, but if you think about it, games and simple 2Dapplications are the programs that most consumers run where speedy performancereally is important. That's why we ran the benchmarks we did; officeenvironments with their servers or workstation PC are more interested instability, and overclocking has an element of risk involved for both hardwareand software.Athlon64 based systems seem to act a lot like the 800 MHz FSB Pentium 4processors in regard to their memory bandwidth and timings when overclocked.However, before conclusions can be drawn in this field, more research has to bedone before....If you're in the market for new memory for your Pentium 4 system and you'reonly thinking about gaming performance, then you're best bet is to get DDR whichis rated to run aggressive timings. Some examples include Mushkin's PC3500 LevelII which is rated to run 2-2-2-5 at 217 MHz FSB or Corsair's TwinX-3200LL whichare rated for 2-2-2-5 at 200 MHz.If you're a newbie/novice overclocker and would prefer to buy something thattakes a little less work while still producing good numbers on your Pentium 4system, then by all means get some of the high speed DIMMs that are available onthe market. They're not quite as fast as the low latency modules as we've shown,but they're much easier to set up. Now for AMD systems, because the AthlonXPcannot hit as high speeds as the Pentium 4 in general, it is always best to pairan AMD processor with nice low latency memory for the best results.For more technical articles go to http://www.tornadocomputers.com echie.php Article Tags: High Speed Memory, Memory Bandwidth, Latency Timings, Dual Channel, High Speed, Speed Memory, About Memory, Memory Timings, Slow Timings, Fast Memory