I'm in the process of upgrading my RAM from 1GB to 2. My motherboard is not overclockable; runs at 266Mhz FSB and at 133Mhz with RAM. The compatible RAM is DDR PC2100 but I currently have a DDR PC3200 400Mhz installed and it works perfectly. In upgrading I'm deciding between a CAS 2.5 and a CAS 3 memory. Would I notice a considerable difference in performance between the two given my configuration? The difference in price is of aboutn $30. Thanks in advance for sharing your knowledge. Ron.

Don't get your numbers confused. Your CPU runs at 133MHz, not 266MHz. 266 is the "effective speed" due to double-pumping. I don't know which Athlon you have, but check the clock settings..you'll find it's [?? x 133MHz], not [?? x 266MHz]. "The compatible RAM is DDR PC2100 but I currently have a DDR PC3200 400Mhz installed" As long as you have it clocked down to 133MHz (DDR266) to match the CPU frequency, you're fine. Anything else & you're losing performance. "In upgrading I'm deciding between a CAS 2.5 and a CAS 3 memory" If your current RAM is CAS-3 & you add CAS-2.5, it will ALL run as CAS-3.

The CPU is and Athlon XP Thoroughbred with 2000Mhz Core Speed, a rated 266Mhz FSB and a 133 Mhz Bus Speed (CPU-Z info). The mobo is an ASUS A7M266-M, chipset AMD-761. I know that if I mixed memory it would run at the lower speed. I am replacing the 2x 512Mb sticks of RAM with 2x1GB new ones. I have a choice of CAS 2.5 or CAS 3 and my question is if there would be a noticeable performance difference between the two. If so then I would spend a little more and get the 2.5 one. If not then I would save my money.

Like I said, don't go by the rated speed (266MHz)...go by the actual frequency of 133MHz. "I know that if I mixed memory it would run at the lower speed." Apparently you don't realize how important it is to run the RAM at the same frequency as the CPU, especially on a socket A system? If you run DDR400 at it's default frequency of 200MHz with your CPU at 133MHz, you're taking a substantial performance hit. There's nothing wrong with running DDR400, provided you clock it down to DDR266 speed (133MHz) to match the CPU. If your BIOS allows full adjustment of memory speed & timings, just get the cheaper DDR400 CAS-3 & manually configure the settings to run as DDR266 CAS-2.5 (2.5-3-3-7).

This should explain: "When looking at the AMD-supporting chipsets async mode are to be avoided at all costs. AMD-supporting chipsets offer less flexibility in this regard due to poorly implemented async modes. Even if it means running our memory clock speed well below the maximum feasible for a given memory, an Athlon XP system will exhibit best performance running the memory in sync with the FSB. To achieve synchronous operation, there is usually a Memory Frequency or DRAM ratio setting in the bios of your system that will allow you to manipulate the memory speed to a either a percentage of the FSB (ie. 100%) or a fraction (or ratio) ie. N/N where N is any integer available to you. Here are some examples: 200MHz FSB speed with 100% or 1:1 (FSB:Memory ratio) results in 200MHz memory speed (DDR400) 200MHz FSB speed with 120% or 5:6 (FSB:Memory ratio) results in 240MHz memory speed (DDR480) 250MHz FSB speed with 80% or 5:4 (FSB:Memory ratio) results in 200MHz memory speed (DDR400) The first example is wholly acceptable for any AMD system, memory should be set this way at all times for best performance. Asynchronous FSB/Memory Speeds are horridly inefficient on AMD systems" http://www.dslreports.com/faq/9223

Jam, I have made it clear in my first post that nothing is adjustable. No overclocking available. I can't change nothing in the BIOS as this feature is not available. My question is simple: Between a Patriot signature CAS3 and Patriot High Performance CAS2.5, given my hardware capability, would I see any performance gain?

Here's a little something for Outlandish to mull over. It comes from our friends over at MADSHRIMPS: "The Core 2 has a front side bus (FSB) speed of 266Mhz x 4 (Quadruple) “1066Mhz”, the ram is running at 266Mhz x2 (Dual Channel) x2 (DDR) = “1066Mhz”, so with PC4200 memory and FSB are running synchronized. When you use PC5300 you are no longer running synchronous with the FSB and a memory divider of x1.25 (5/4) has to be used. The older Athlon XP from AMD also displayed this decrease in performance when running memory asynchronous due to its short pipeline, where memory latency is more important then memory bandwidth. With the Pentium 4 the pipeline was longer and the effect of running asynchronous which increased latency was masked. Core 2 technology marked Intel's return to a shorter pipeline and thus is more similar to the Athlon XP than the Pentium 4. By running the memory synchronous to the FSB you have the least amount of latency and thus performance is at its best." http://www.madshrimps.be/?action=ge...