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DRAM General Knowledge FAQ:

Q: What is DDR SDRAM?
A: DDR SDRAM, Double Data Rate Synchronous Dynamic Random-Access Memory (or DDR2, DDR3 & DDR4 SDRAM) , is the most common kind of memory integrated circuits for personal computers and workstations. Memory is the network of electrically-charged points in which computer stores quickly accessible data in forms of 0s and 1s. Random-access means that PC processors can access any part of the memory directly without having to proceed consecutively from a point. DRAM, in opposite to SRAM (Static RAM), needs to have its storage cells refreshed or given a new electronic charge periodically. It loses its data as soon as power is removed. Performance of a DDR SDRAM is determined by data transfer rates, which are affected by the timing of the electrical data and clock signals. A DDR SDRAM with a certain clock frequency achieves bandwidth of a single data rate SDRAM running at the same clock frequency, because a DDR SDRAM supports data transfer at both edges of clock cycle. Bandwidth is the term representing the available or consumed data communication resources expressed in bits per second. A clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronometo coordinate actions of circuits.

Q: What is Dual Channel Memory?
A: Dual channel architecture simply takes the existing RAM technology to break the single channel bottleneck of memory bandwidth. With a second parallel channel added into chipset, the bandwidth of memory has greatly increased to boost up overall system performace. In order to use Dual Channel Memory, your motherboard has to be capable of supporting this technique and you will also need two equal memory modules.

Q: What is CAS Latency?
A: Besides the speed of DDR1,DDR2 and DDR3, there is additional information that tells you the memory performance. Those information are numbers like 9-9-9-28, and the lower the better 7-7-7-24. CL: CAS Latency. The time it takes between a command having been sent to the memory and when it begins to reply to it. It is the time it takes between the processor asking for some data from the memory and it returning it. tRCD: RAS to CAS Delay. The time it takes between the activation of the line (RAS) and the column (CAS) where the data are stored in the matrix. tRP: RAS Precharge. The time it takes between disabling the access to a line of data and begin of the access another line data. tRAS: Active to Precharge Delay. How long the memory has to wait until the next access to the memory can be initiated. CMD: Command Rate. The time it takes between the memory chip having been activated and when the first command may be sent to the memory. Sometimes this value is not informed. It usually is T1 (1 clock cycle) or T2 (2 clock cycles).

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