The memory of the system is its ability to retain data for a period of time and it can be built right into other system board. But usually, it is attached to the board in the form of a chip or module.
The main system memory is random access memory or RAM, in short and the data contained in it can be accessed in random. The main type of system memory that is used today is synchronous dynamic RAM (SDRAM). But double data rate SDRAM has become the standard for most of the systems.
Occasionally, Ram Bus Dynamic RAM or DDR2 are used which is slightly different. SDRAM is different since it waits for each computing cycle before responding to inputs. DDR memory is quite similar to traditional SDRAM except that it transfers data twice during each clock cycle which, in effect, doubles the transfer rate of memory, while the system bus remains the same. Hence a hundred MHz system bus that handles DDR memory can effectively use 200 MHz RAM.
DDR is available in various speeds, each with two designations. Memory is quite easy to install in system but the correct type of memory has to be purchased. The system memory upgrades should be compatible with the memory present already, as also, with the motherboard of the computer.
Additionally, it is crucial to know which type SDR or DDR SDRAM and speed of memory the system uses and purchase the same type while upgrading or replacing the memory. This can be found from the manual or from the manufacturer.