They are 5V and 3.3V, and they are not interchangeable. However these are only rated for 66MHz bus operation. It enables RAM manufacturers to make chips that would work with Intel BX processor chip-set with an over 100MHz system bus speed. Nevertheless, it requires significant changes in the motherboard design to adopt such technology. Cells are refreshed one row per refresh cycle.
Refresh rate is the number of rows that have to be refreshed.
They differ in the way they are laid out and accessed. It is the waiting time for the system to read the first data from the main memory. It is used to detect errors occurred in memory. It can only detect errors but not correct errors. It also has problem in handling multiple bits error in a single byte of data.