Making sense of all of the numbers related with memory types and modules can be quite cumbersome if you have no experience or knowledge. If you take a look at the product information listed by an online retailer, many people don't quite no where to start or how to match up what information they have about their motherboard with what the product list information provides. This thread is a crash course in memory. EDO RAM - Extended Data Out Random Access Memory - 3.3V - 72 Pins SD RAM - Single Data Random Access Memory - 3.3V - 168 Pins DDR RAM - Double Data Rate Synchronous Dynamic Random Access Memory - 2.5V - 184 Pins DDR2 RAM - Double Data Rate Two Synchronous Dynamic Random Access Memory - 1.8V - 240 Pins RAMBUS or RDRAM was a memory standard used by some legacy Intel chipset solutions. What does system memory do? Your CPU and hard drive are constantly communicating with one another. Random Access Memory, or system memory is their go-between. It speeds up communication. When the computer is turned off or restarted, anything in RAM is erased. Data is actually transferred from the processor to the L1 cache on the processor to the L2 cache on the processor and then on to the system memory and then the hard drive. Therefore, upgrading your RAM is potentially the most cost-effective upgrade you can do! Notes on dual channel DDR SDRAM describes a motherboard technology that effectively doubles data throughput in the frontside bus from RAM to the memory controller. DDR-enabled memory controllers utilize two 64-bit data channels, resulting in a total bandwidth of 128 bits, to move data from RAM to the CPU. In order to achieve this, the DDR SDRAM memory modules must be installed into matching memory slots, which are usually color coded on the motherboard. Each memory module in each slot should be identical to the one in its matching slot.It's also possible to use similar memory sticks from different manufacturers or different production series as long they are of the same size, specification, the same number of memory chips and internal organisation. The above is the Wikipedia definition of Dual Channel... The VIA KT880 was the first dual channel VIA chipset, featuring a DualStream64 Dual Channel memory bus for DDR400/333 SDRAM Synchronous Dynamic Random Access Memory is a new form of DRAM that can be coordinated or synchronized to the clock speed of the computer. The KT880 was also the last VIA chipset released for the AMD K7 line of CPUs. All K8 chipsets (K8T800, K8T800Pro, K8T890) have the memory controller integrated into the AMD 64 processor instead of the chipset North Bridge. Some AMD 64 CPUs feature a single channel memory controller and some feature a dual channel memory controller. On the Intel platform side of things, the VIA PT880 was the first VIA chipset for the Intel P4 to feature the DualStream64 Dual Channel memory bus for DDR400/333 SDRAM. If your mainboard or AMD 64 CPU does feature a dual channel memory controller it is highly recommended that you purchase matched pairs only. A matched pair are two modules with exactly the same size, speed, latency and timings. Using matched pairs ensures that the chipset and/or CPU can access the modules with the greatest efficiency. A lot of major brand memory manufacturers sell memory "kits" especially labeled for dual channel memory use. Timings Speaking of which, there is more info on CAS Latency and timings Here. Keeping yourself up to date with the latest developments is also pretty important. Thankfully you can get away with knowing the basics about the most crucial timing, CAS latency. CAS stands for Column Address Strobe and the CAS Latency timing referred to on memory module specifications and price lists represents the number of cycles that the data waits before it delivers the data. The lower the CAS latency the quicker the data is transferred. CAS latency timing however is of course influenced by the speed of the memory. DDR400 CL3 running at 200MHz leaves a latency of 15ns. The tables linked will allow you to see which speed of RAM is faster at different CAS ratings. http://i33.photobucket.com/albums/d89/pelvis_3/timings.gif Conclusion Having determined what motherboard you have, you take note of the memory types supported. A board that supports SDRAM cannot support DDR and DDR2 modules. As of last time i checked, only the VIA PT880Pro chipset can support either DDR or DDR2 RAM (but not both at the same time). All other boards based on other chipsets support either DDR or DDR2 RAM but not both. When you look to purchase RAM,buy a speed that is supported by your motherboard, or a faster speed. You can for example, buy DDR400 PC32000 RAM for use in a mainboard that lists support for DDR266/333 RAM only. Simply plug it in and it will run at the highest speed that your motherboard is compatible with. Although it's more expensive to purchase higher speed modules, it allows for the possibility of overclocking them, using them in a newer system later down the track and also possibly increases stability. A module running at a lower speed than what it is rated for is often more stable than a module running at it's rated speed. Having said that, take note of the CAS latency rating of the modules. High speed (often unofficial) modules often have such a high CAS latency that any performance gain there may have been in speed is lost in latency. - Note - It is common practice to increase the voltage provided to RAM to provide higher performance settings - not only FSB speeds but also reducing the CAS timings to increase performance. A voltage of at least 2.7 for high performance DDR RAM Random Access Memory is recommended. Default is 2.5v. The majority of the motherboards that i've used, I set to at least 2.7V, 0.2V above the default setting. This increases stability and does not normally harm the modules - End of Note - The best piece of advice to give you is to always buy brand modules from a trusted retailer. Don't buy generic or no-name RAM. Try to match any old modules you may already have with the same brand and specifications but keep in mind that every brand uses different memory chips. It is the memory chips that are most important to match up. The chip types are not normally listed at point of sale. You would need to look on the memory manufacturer's web site or on the RAM itself for the details of a model number to get that information. If you have 512MB and you want to upgrade to 2GB your best bet would be either: 1. Get another 3 matching 512MB modules or 2. Purchase 2 brand new 1GB modules. Two matching 1GB modules will provide better stability and performance unless you can match model and chips with the original 512MB module. Mixed RAM and insufficient voltage to RAM are some of the most common causes of system instability. There is so much that can be said about system memory. What I have tried to cover here is the information that the average user needs to know about in order to choose RAM that is compatible with their system, plus some extra information to help them make an informed decision about the type of modules they should choose. pelvis_3
Correct me if I'm wrong, but doesn't Direct Memory Access work so that data flows from the hard drive directly to the RAM instead of going through the CPU? Or is that only for memory access for other peripherals.
If it's enabled, yes. DMA is intended to be used in low power mode because it uses the same memory bus as the CPU and only one or the other can use the memory at the same time, but it has limits to it's flexibility!
