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Extended data out (EDO) is a modified form of Fast Page Mode (FPM) memory, common in the 1980s and 1990s that allows timing overlap between each new data access cycle.
In EDO, a new data cycle is started while the data output of the previous cycle is still active. This process of cycle overlapping, called pipelining, increases processing speed by about 10 nanoseconds per cycle,increasing computer performance by about 5 percent compared to performance using FMP.
EDO has now been replaced by synchronous DRAM (SDRAM) and other memory technologies.
Extended Data Out is also known as Hyper Page Mode enabled DRAM.
EDO was first introduced in 1995 with the Intel 430FX chipset and quickly became prevalent. EDO allows burst systems of 5-2-2-2 at 66MHz when a chipset is optimized. It is also used to support on-board RAM, which is compatible with several expansion boards.
Extended data out is faster than fast-page mode because it eliminates delay. FPM needs a delay before the memory controller transmits the next memory address. The EDO memory contains a special chip that allows timing overlap between continuous accesses. The data output drivers on the chip stay on when the memory controller eliminates the next cycle column address. This process allows the next cycle to intersect the earlier cycle.
EDO does this by starting the data output on the falling edge of the column address strobe (/CAS). The output continues even when the /CAS rises again. EDO extends the data output time by holding the output valid until the /CAS falling edge chooses another column address, or until the row address strobe (/RAS) is deasserted.
EDO brought increased abilities and proficiencies, permitting a sort of replacement for L2 cache, which is used by the CPU to decrease the average time to access memory. Because it increases L2 cache performance, EDO proved for notebooks with a limited form factor and battery life restrictions.
EDO is now an obsolete technology having been superseded by several generations of memory hardware.