SIMM RAM FPM and EDO RAM

Fast page mode DRAM is also called FPM DRAM, Page mode DRAM, Fast page mode memory, or Page mode memory.

In page mode, a row of the DRAM can be kept "open" by holding /RAS low while performing multiple reads or writes with separate pulses of /CAS so that successive reads or writes within the row do not suffer the delay of precharge and accessing the row. This increases the performance of the system when reading or writing bursts of data.

Static column is a variant of page mode in which the column address does not need to be strobed in, but rather, the address inputs may be changed with /CAS held low, and the data output will be updated accordingly a few nanoseconds later.

Nibble mode is another variant in which four sequential locations within the row can be accessed with four consecutive pulses of /CAS. The difference from normal page mode is that the address inputs are not used for the second through fourth /CAS edges; they are generated internally starting with the address supplied for the first /CAS edge.

EDO DRAM, sometimes referred to as Hyper Page Mode enabled DRAM, is similar to Fast Page Mode DRAM with the additional feature that a new access cycle can be started while keeping the data output of the previous cycle active. This allows a certain amount of overlap in operation (pipelining), allowing somewhat improved performance. It was 5% faster than Fast Page Mode DRAM, which it began to replace in 1995, when Intel introduced the 430FX chipset that supported EDO DRAM.

To be precise, EDO DRAM begins data output on the falling edge of /CAS, but does not stop the output when /CAS rises again. It holds the output valid (thus extending the data output time) until either /RAS is deasserted, or a new /CAS falling edge selects a different column address.

Single-cycle EDO has the ability to carry out a complete memory transaction in one clock cycle. Otherwise, each sequential RAM access within the same page takes two clock cycles instead of three, once the page has been selected. EDO's performance and capabilities allowed it to somewhat replace the then-slow L2 caches of PCs. It created an opportunity to reduce the immense performance loss associated with a lack of L2 cache, while making systems cheaper to build. This was also good for notebooks due to difficulties with their limited form factor, and battery life limitations. An EDO system with L2 cache was tangibly faster than the older FPM/L2 combination.

Single-cycle EDO DRAM became very popular on video cards towards the end of the 1990s. It was very low cost, yet nearly as efficient for performance as the far more costly VRAM.

Much equipment taking 72-pin SIMMs could use either FPM or EDO. Problems were possible, particularly when mixing FPM and EDO. Early Hewlett-Packard printers had FPM RAM built in; some, but not all, models worked if additional EDO SIMMs were added.

Sizes Mb ranged from 1Mb to about 128Mb.
They were either Single Sided or Dual Sided.
They had 72 pin connectors and 1 notch.