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Memory refresh is a process of periodically reading information from an area of computer memory and immediately rewriting the read information to the same area without modification, for the purpose of preserving the information. [1]
DDR4 is not compatible with any earlier type of random-access memory (RAM) due to different signaling voltage and physical interface, besides other factors. DDR4 SDRAM was released to the public market in Q2 2014, focusing on ECC memory , [ 6 ] while the non-ECC DDR4 modules became available in Q3 2014, accompanying the launch of Haswell-E ...
Memory scrubbing consists of reading from each computer memory location, correcting bit errors (if any) with an error-correcting code , and writing the corrected data back to the same location. [ 1 ] Due to the high integration density of modern computer memory chips , the individual memory cell structures became small enough to be vulnerable ...
DDR SDRAM (sometimes called DDR1 for greater clarity) doubles the minimum read or write unit; every access refers to at least two consecutive words. Typical DDR SDRAM clock rates are 133, 166 and 200 MHz (7.5, 6, and 5 ns/cycle), generally described as DDR-266, DDR-333 and DDR-400 (3.75, 3, and 2.5 ns per beat).
Double data rate SDRAM (DDR SDRAM or DDR) was a later development of SDRAM, used in PC memory beginning in 2000. Subsequent versions are numbered sequentially (DDR2, DDR3, etc.). DDR SDRAM internally performs double-width accesses at the clock rate, and uses a double data rate interface to transfer one half on each clock edge. DDR2 and DDR3 ...
A memory rank is a set of DRAM chips connected to the same chip select, which are therefore accessed simultaneously. In practice all DRAM chips share all of the other command and control signals, and only the chip select pins for each rank are separate (the data pins are shared across ranks).
Double data rate (DDR) memory controllers are used to drive DDR SDRAM, where data is transferred on both rising and falling edges of the system's memory clock.DDR memory controllers are significantly more complicated when compared to single data rate controllers, [citation needed] but they allow for twice the data to be transferred without increasing the memory's clock rate or bus width.
The time to read the first bit of memory from a DRAM without an active row is T RCD + CL. Row Precharge Time T RP: The minimum number of clock cycles required between issuing the precharge command and opening the next row. The time to read the first bit of memory from a DRAM with the wrong row open is T RP + T RCD + CL. Row Active Time T RAS