RAM is an acronym for Random Access Memory that is also known as volatile memory, because the data it holds is lost when the desktop PC or laptop/notebook computer using it is switched off. Briefly, RAM memory is used by the system to store data in the form of files for processing by a computer's central processing unit (CPU), also known as the processor. The processors used in most PCs are made by Intel and AMD. The processor runs the program and data files according to instructions given to it by the operating system, which, on PCs, is usually a version of Windows, or, to a much lesser extent, a version of Linux.
Dynamic RAM (DRAM)
Dynamic RAM is a type of RAM that only holds its data if it is continuously accessed by special logic called a refresh circuit. Many hundreds of times each second, this circuitry reads the contents of each memory cell, whether the memory cell is being used at that time by the computer or not. Due to the way in which the cells are constructed, the reading action itself refreshes the contents of the memory. If this is not done regularly, then the DRAM will lose its contents, even if it continues to have power supplied to it. This refreshing action is why the memory is called dynamic.
Static RAM (SRAM)
Static RAM is a type of RAM that holds its data without external refresh, for as long as power is supplied to the circuit. SRAMs are used for specific applications within the PC, for which it is perfectly suited; cache memory needs to be very fast, and not very large. SRAM is manufactured in a way rather similar to how processors are: highly-integrated transistor patterns photo-etched into silicon. Each SRAM bit is comprised of between four and six transistors.
FPM RAM
FPM RAM, which stands for Fast Page Mode RAM is a type of Dynamic RAM (DRAM). The term Fast Page Mode comes from the capability of memory being able to access data that is on the same page and can be done with less latency. Most 486 and Pentium based systems from 1995 and earlier use FPM Memory.
EDO RAM
EDO RAM, which stands for Extended Data Out RAM came out in 1995 as a new type of memory available for Pentium based systems. EDO is a modified form of FPM RAM which is commonly referred to as Hyper Page Mode. Extended Data Out refers to fact that the data output drivers on the memory module are not switched off when the memory controller removes the column address to begin the next cycle, unlike FPM RAM. Most early Penitum based systems use EDO.
SDRAM
SDRAM , which is short for Synchronous DRAM is a type of DRAM that runs in synchronization with the memory bus. Beginning in 1996 most Intel based chipsets began to support SDRAM which made it a popular choice for new systems in 2001.
SDRAM is capable of running at 133MHz which is about three times faster than FPM RAM and twice as fast as EDO RAM. Most Pentium or Celeron systems purchased in 1999 have SDRAM.
DDR RAM
DDR RAM, which stands for Double Data Rate which is a type of SDRAM and appeared first on the market around 2001 but didn’t catch on until about 2001 when the mainstream motherboards started supporting it. The difference between SDRAM and DDR RAM is that instead of doubling the clock rate it transfers data twice per clock cycle which effectively doubles the data rate. DDRRAM has become mainstream in the graphics card market and has become the memory standard.
DDR2 RAM
DDR2 RAM, which stands for Double Data Rate 2 is a newer version of DDR which is twice as fast as the original DDR RAM. DDR2RAM came out in mid 2003 and the first chipsets that supported DDR2 came out in mid 2004. DDR2 still is double data rate just like the original DDR however DDR2-RAM has modified signaling which enables higher speeds to be achieved with more immunity to signal noise and cross-talk between signals.
RAMBUS (RIMM) RAM
RAMBUS RDRAM is a type of ram of its own, it came out in 1999 and was developed from traditional DRAM but its architecture is totally new. The RAMBUS design gives smarter access to the ram meaning that units can prefetch data and free some CPU work. The idea behind RAMBUS RAM is to get small packets of data from the RAM, but at very high clock speeds. For example, SD RAM can get 64bit of information at 100MHz where RAMBUS RAM would get 16bits of data at 800MHz. RIMM ram was generally unsuccessful as Intel had a lot of problems with the RAM timing or signal noise. RD RAM did make an appearance in the Sony Playstation 2 and the Nintendo 64 game consoles.
Fundamentally, computers just deal with numbers. They store letters and other characters by assigning a number for each one. Before Unicode was invented, there were hundreds of different encoding systems for assigning these numbers. No single encoding could contain enough characters: for example, the European Union alone requires several different encodings to cover all its languages. Even for a single language like English no single encoding was adequate for all the letters, punctuation, and technical symbols in common use. 
