What is DRAM?
Dynamic memory is named as such because the information stored in each capacitor eventually leaks, which requires a periodic refresh. In other words, the memory is not static. DRAM is unique from static memory in that the structure is much simpler. DRAM uses one capacitor and one transistor per cell, whereas static memory uses at least four of each per cell. This makes DRAM cheaper to produce and easier to develop higher capacity memory modules.
DRAM also comes in many different sizes, making it suitable for different motherboard configurations. If you’ve ever shopped for sticks of RAM, you are probably familiar with sizes like 512MB, 1GB, or 2GB sticks. These numbers relate to the available storage space on the memory module. RAM should be bought in uniform sizes, unless you know your motherboard can handle varying sizes.
RAM also comes in different pin types, like DIMM or SDRAM. The pin type references how the memory modules connect to the available motherboard slot. DIMM stands for Dual Inline Memory Modules. The DIMM modules replaced the SIMM and RIMM modules of yesteryear. SDRAM modules have varying number of pin contacts on each side. They come in configurations of 20, 60, or 88 pin configurations on each side, totaling 168 pins all together.
DIMM memory modules are not the same size as SDRAM modules. DIMM modules have 184 pins compared to SDRAM’s 168. Obviously, this makes them incompatible in the same motherboard. Most of today’s motherboards utilize the SDRAM standard, not the DIMM. Although DIMMs are still often found in large server constructs. To determine the type of RAM your system uses, you can view the module model for specifications, or you can look at the physical notches on the module. SDRAM modules have two notches while DIMMs have only one.
RAM also relies on timing, which affects how quickly the RAM can access the columns and rows of data stored on the chip. We’ll go into greater detail on timings in a moment, but we can review the DDR, DDR2, DDR3 technology.
What is DDR?
DDR stands for Double Data Rate. DDR memory utilizes the timing clock in such a way to double the amount of transferable data in the same amount of time as regular RAM. To really understand DDR RAM, we need to look at how timing works in memory modules.
In computers the timing regulates on an oscillating frequency. Think of the timing as a pendulum on a wall clock. For regular single data RAM sticks, during the upswing of the pendulum, data gets transferred. In DDR memory modules, they transfer data during both the upswing and downswing of the clock.
There are five versions of DDR RAM, including PC1600, PC2100, PC2700, PC3200, and PC4000. The number refers to the amount of bandwidth the module allows; in other words, it’s related to the module’s potential bandwidth. A PC2100 memory module would be able to carry up to 2.1GB of data per second. This would be meeting the full potential of the memory module without overclocking it. The bandwidth is only a portion of the equation though. Memory modules also have corresponding front side bus speed – the speed at which they can relay information back to the CPU. Since DDR is dual rated, the PC1600 = 2 x 100MHz, PC2100 = 2 x 133MHz, PC2700 = 2 x 166MHz, PCC3200 = DDR400, and PC4000 = DDR500. The Wikipedia.org article on DDR SDRAM gives a clear look at determining the transfer rate.