Different types of RAM's :
RAM is the acronym for 'random access memory' and is usually calculated in megabytes. A RAM chip is a module that holds freshly accessed information so that the central processing unit can have access to it. It is faster than reading from the hard drive and allows for easy access of recently stored data, information, and files. This means that all programs must be run through the RAM before they are usable.
There are two basic types of RAM, namely dynamic RAM and static RAM. A dynamic RAM is called so because it has to be constantly refreshed by the memory controller. The reason for refreshing is that the capacitors that hold the information or data have a built-in leak that can only be stopped by refreshing the information thousands of times in a second. This makes dynamic RAM slower and cumbersome compared to static RAM.
FAM RAM:
Fast Page Mode RAM was one of the earlier RAM models. This chip was introduced in 1990.FPM RAM operated at a clock speed of 25 megahertz, or MHz. The FPM RAM came in 30-pin and 72-pin models. It was able to achieve speed by using only the column address when the data was located in the same row as the previously accessed data.
EDO RAM:
Extended Data Out RAM was introduced in 1994. This chip operated at a clock speed of 50 MHz. EDO RAM was used with the earlier models of Intel Pentiums prior to Pentium 4. EDO RAM had 72 Pins. This RAM was able to achieve faster speeds than FPM RAM by overlapping access cycles using the output buffer.
SD RAM :
Synchronous Dynamic Random Access Memory had 168 pins. First shipped models operated at 66 MHz and later models had a speed of 100 MHz and then 133 MHz. SDRAM was introduced in 1996. This was the first RAM chip to synchronize with the microprocessor's clock speed.
DDR SDRAM :
Double Data Rate SDRAM had 184 pins. Compatible with AMD and Intel microprocessors faster than 1 GHz, it improved on SDRAM and operated at clock speeds as fast as 266 MHz. It was twice as fast as SDRAM because it triggered off both the rising and falling edge of the clock signal. SDRAM on the other hand, used only the rising edge of the clock signal.