• SDRAM is one of the most common RAM types.barrettes de m??moire image by Melisback from Fotolia.com
  
  Since the beginning of the home computer industry, personal computers have required Random Access Memory (RAM). When a program runs, program data moves from the hard drive--or the floppy drive, in older computers--to the RAM, where it resides until the program ends. Even the operating system requires RAM to run. RAM technology has evolved greatly over the years, with new forms of RAM being introduced almost as often as new processor technologies.
  
  

Dual Inline Package (DIP)

• Computer owners today think of RAM as having the form of a small card with several chips. A DIP is just one of those chips. For many early PCs, the process of upgrading the RAM involved pushing DIPs into sockets on the motherboard or an add-on card. This process was difficult to do correctly, and DIP pins were easily bent or broken off.
  
  

Single Inline Memory Module (SIMM)

• SIMMs improved the process of installing memory by making DIPs permanent parts of a small expansion board. SIMMs resemble the memory modules that we use today, except that they are shorter in size. SIMMs can have either 30 or 72 metal connectors on the bottom and are generally installed in matched sets of two or four. 30- and 72-pin SIMMs are common in computers containing 386, 486 and Pentium processors.
  
  

Synchronous Dynamic Random Access Memory (SDRAM)

• SDRAM is packaged in the Dual Inline Memory Module (DIMM) format, which has 168 metal connectors on the bottom. SDRAM is able to transfer data during each "tick" of the system bus clock. For example, if the system bus rate is 100 MHz, SDRAM can transfer data 100 million times per second. Standard SDRAM speeds scale up to 133 MHz, and SDRAM is common in computers containing Pentium II and Pentium III processors.
  
  

Direct Rambus DRAM (DRDRAM)

• For a short time in the early 2000s, Intel intended to utilize DRDRAM with all Pentium 4-based computers. DRDRAM, designed and licensed by Rambus, had much higher bandwidth than SDRAM. However, it also had higher latency and cost more than SDRAM and the newer emerging standard, Double Data Rate SDRAM. Consumers' unwillingness to pay the higher cost of DRDRAM threatened to slow the adoption of the Pentium 4 processor among PC enthusiasts, and Intel eventually relented and provided DDR-SDRAM Pentium 4 chipsets.
  
  

Double Data Rate SDRAM (DDR-SDRAM)

• As the name implies, DDR-SDRAM transfers double the amount of SDRAM at a given clock rate. This is accomplished by transferring data twice per clock cycle rather than once. Each new RAM technology since DDR-SDRAM has been an evolution of that same idea. DDR2-SDRAM transfers data four times for each clock cycle, and DDR3-SDRAM doubles the transfer rate again to eight times per clock cycle. As of 2010, most current computers utilize either DDR2-SDRAM or DDR3-SDRAM.