Extended Data Out (EDO)

What is Extended Data Out (EDO)?
Extended Data Out (EDO) is a modified form of Fast Page Mode (FPM) memory that was common in the 1980s and 1990s and allows a time overlap between each new data access cycle.

A new data cycle is started in EDO while the data output of the previous cycle is still active. This process of cycle overlap, known as pipelining, increases processing speed by about 10 nanoseconds per cycle, increasing computing power by about 5 percent compared to FMP.
EDO has now been replaced by synchronous DRAM (SDRAM) and other memory technologies. Extended Data Out is also known as Hyper Page Mode Capable DRAM.

EDO was first introduced in 1995 with the Intel 430FX chipset and it spread quickly. EDO enables burst systems of 5-2-2-2 at 66 MHz if a chipset is optimized. It is also used to support on-board RAM that is compatible with multiple expansion cards.

Expanded data is faster than the fast page mode because it eliminates the lag. FPM needs a delay before the memory controller transmits the next memory address. The EDO memory contains a special chip that enables a temporal overlap between continuous accesses. The on-chip data output drivers remain on when the memory controller removes the column address of the next cycle. 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). Output continues even if / CAS rises again. EDO extends the data output time by holding the output valid until the falling edge of / CAS selects a different column address or until the row address strobe (/ RAS) is deactivated.

EDO brought increased skills and abilities with it, allowing for some sort of replacement for the L2 cache used by the CPU to reduce the average time to access memory. Because it increases L2 cache performance, EDO has proven its worth for notebooks with a limited form factor and limited battery life.

EDO is now an outdated technology that has been superseded by several generations of storage hardware.