All computers require memory to function. The main memory of the computer is random access memory, or RAM for short. It is so named because the data it contains can be accessed in any order or in random order. It is produced on small circuit boards in the form of sticks, which are often called memory sticks. Information is stored in memory while it waits to be processed by the central processing unit, or CPU. Having the correct memory type and speed is essential to ensure your system runs optimally.
The main type of memory used in desktop computing systems today is Synchronous Dynamic RAM (SDRAM). In recent years, Double Data Rate SDRAM (DDR SDRAM, or simply DDR) has become the standard for most systems, and older memory is now referred to as Single Data Rate (SDR). SDRAM). Occasionally systems use Rambus Dynamic RAM (RDRAM) or DDR2 RAM, which are slightly different and beyond the scope of this article.
SDRAM is different from other forms of asynchronous memory in that it waits every clock or computation cycle before responding to inputs. These clocks happen very fast in computers (millions of times per second), but still the speed of memory is ultimately limited by the computer’s bus. This is the wiring on the main motherboard or in the system that connects all the components. Both the processor and memory can handle high clock speeds, but if the system bus speed is low, they will be limited by the lower speed. It is important that they all operate at similar speeds in order to operate most efficiently. For example, SDR SDRAM comes in PC66, PC100, and PC133; these numbers refer to the RAM clock speed in megahertz (one million cycles per second): 66 MHz, 100 MHz, and so on. If the system bus speed is 100 MHz and the memory is 66 MHz, then the memory is not running as fast as it could and PC100 memory should be purchased. Of course, if PC133 were purchased for this same system, the extra 33 MHz would simply be wasted because the system bus can only handle 100 MHz.
Double Data Rate (DDR) memory is very similar to traditional SDRAM, except that it transfers data twice during each clock cycle. This doubles the memory transfer rate while the system bus remains the same. Therefore, a 100 MHz system bus driving DDR memory can effectively use 200 MHz RAM. DDR comes in many speeds, each with two designations. On the box or somewhere in the specifications, the memory will be referred to as DDR-xxx, where xxx is replaced by the effective clock speed of the memory, such as 200 as in the example above. It will also display a number of PC-xxxx, where xxxx represents the bandwidth of all memory. This is not particularly important for newbies to understand. The most common are: DDR-200/PC-1600, which operates at a clock speed of 100 MHz (effectively 200 MHz), DDR-266/PC-2100, which operates at 133 MHz (effectively 266 MHz), DDR- 333/PC-2700, which runs at 166 MHz (333 MHz) and DDR-400/PC-3200, which runs at 200 MHz (400 MHz).
It is very important to know what type (SDR or DDR SDRAM) and speed of memory your system uses and to always purchase this type when upgrading or replacing your memory. You can usually find this information in the manual or contact the manufacturer.