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Not All Memory is Created Equal

Part I: Background and Memory Types


Most people who have or are planning on purchasing a computer know to look for certain things. One of those things is the amount of memory or RAM that comes in a computer. The higher the amount of RAM, the better the system. What a lot of people don't know is that the type of memory that goes into a computer can also make a big difference in the performance and future ability to upgrade that system.

Some Background

Before really talking about memory and what to look for, it is important to talk about the other components in a computer that interact with the memory. In particular, there are two primary pieces that determine the memory that is used in a computer, the CPU and the motherboard or chipset.

All CPUs have a speed rating given to them. This is often the rating of the processor in gigahertz. There is a second speed rating to the processor referred to as the front side bus. The front side bus refers to the speed at which the processor can talk to the memory and other components on the system. The processor speed is actually a multiplier of the front side bus speed. For example, an Intel Core 2 Duo E6400 CPU has a 1066 MHz front side bus which is multiplied by 2 to generate the 2.13 GHz speed. Even though the front side bus is 1066 MHz, the memory interface runs at a fraction of this due to memory not running to such high speeds when it was released.

Now the motherboard also determines a lot about the memory. The chipset that interacts with both the CPU and the memory is designed to work with specific memory types and sizes. While the chipset may be able to support a processor such as the Intel Core 2 Duo mentioned before, it might only support memory up to speeds of 533MHz. Also, these chipsets are generally designed to communicate with memory up to a specific size, such as a 2GB DIMM modules. This coupled with the motherboard layout will determine the maximum amount of memory a system can hold. If the system has 2 slots, then the maximum would be 4 gigabytes of RAM which is less than a separate board which can support 4 modules resulting in 8 gigabytes of RAM.

Therefore, before you start looking at the memory, do research and make sure you know how many memory modules your motherboard can support as well as the maximum speed of the memory it can hold. This will help you to determine what the best mix of memory modules in a system will provide you when the system is first purchased and for when you plan any future upgrades.

Memory Types

While there are many different types of memory on the market, the most common types that are used in PCs right now are:

  • Double Data Rate DRAM (DDR)
  • Double Data Rate 2 DRAM (DDR2)
  • Double Data Rate 3 DRAM (DDR3)

Double data rate or DDR memory is designed to function at two memory operations per clock cycle. This effectively doubles the speed of the memory over older synchronous memory modules. This memory type has been phased out in favor of the high clocked DDR2 standard.

DDR2 is an updated version of DDR that provides even faster clock speeds than the previous DDR memory standard. The two types of memory are not interchangable as they interface with the chipset and memory in a different method. To differentiate the two, each type has a different pin count and layout for the memory modules.

DDR3 is the latest version of memory to be released and once again provides speeds faster than those of DDR2. It is still fairly uncommon but will likely gain more acceptence over time as processor speeds increase requiring the faster memory. For more details about this memory, check out my DDR3 Memory Technology article.

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