Extended Data-Out (EDO) is a DRAM chip technology which improves memory performance 10 to 15% over equivalent Fast Page Mode devices.
Computer systems must be designed to take advantage of this performance increase EDO offers.
Intel’s Triton Chip set, used in Pentium-class computers, are designed to do just that. EDO memory may be installed into most other computer systems but they will function and perform as a Fast Page Mode memory module.
How does EDO Work?
DRAM’s are designed as a matrix of bits. Each bit is accessed by a row and column address. A memory controller inside a computer system provides those addresses to access the data that each bit contains.
A 60ns DRAM will provide that data to the memory controller within 60ns. But there are certain time constraints for the memory controller to set-up the addresses, receive the data, and prepare for the next cycle. An entire memory cycle can range from 85 to 120ns.
Fast Page Mode can decrease cycle times by allowing the memory controller to access other data bits which are in the same row address. This saves time by not having to set up the next row address instruction. Data accessed in the same row is referred to as a “page”.
Extended Data-Out (EDO) can improve cycle times even further by allowing the memory controller to begin a new column address instruction while it is reading data at the current address. Unlike FPM, the data output drivers are not turned off when the memory controller removes the column address to begin the next cycle. This saves approximately 10ns per cycle.
Do EDO SIMMS Look Different? EDO SIMMS look very much like a standard SIMM. Only the type of DRAM chip used on the module is different.