RAM stands for "random access memory." RAM is the temporary data storage in a computer which is accessed directly by the central processing unit (CPU). Computers require RAM in order to process data and run programs. It's much faster for a computer to get its information from RAM than from the hard drive.
The most common type of RAM is Double Data Rate Synchronous Dynamic RAM (DDR SDRAM.) It operates at about double the bandwidth of single-rate SDRAM. Rambus RAM is designed be considerably faster than ordinary RAM. Rambus RAM is rarely used since it's expensive and can only be installed in certain Intel motherboards. RAM comes in different sizes, typically ranging from 256 megabytes (MB) to 2 gigabytes (GB).
RAM comes in long, slender modules with metallic pins at the bottom. Single Inline Memory Modules (SIMMs) typically come with chips on one side whereas Dual Inline Memory Modules (DIMMs) have chips on both sides. DIMMs also have pin connectors on both sides of the module, doubling the number of connections.
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RAM modules are printed circuit boards that plug into the motherboard. Every RAM module has chips that are integrated into the surface of the circuit board. DIMMs can be used singly but SIMMs must be used in pairs. RAM is erased every time your computer is turned off. By comparison, read only memory (ROM) and data stored on the drives are retained after the computer is deactivated. The computer loads programs back into RAM from read only memory and the disk drives the next time it's powered on.
A computer's processor uses RAM to access programs and data it needs to process. Adding more RAM can dramatically increase the speed of your computer. If you are experiencing system slowdowns, you may need to upgrade your RAM. This is especially true if you're hearing a lot of hard drive activity during the slowdowns. This type of activity is commonly called "thrashing" and is an indication that your computer is using the page file on your hard drive as a method to supplement an inadequate amount of RAM.
Most computer users experience the best results by using non-error correction (non-ECC) unbuffered DDR SDRAM. While other types of memory, such as static RAM (SRAM), Rambus RAM and ECC RAM may offer increased performance, their costs are far too high for the benefits gained. Also, adding more memory to your system will achieve better performance boosts than adding faster memory. Furthermore, many computer manufacturers dictate the speed of memory you can install and attempting to install faster memory can backfire. To stay on the safe side, check your computer or motherboard's user guide or website for the RAM specifications, and get exactly the RAM they recommend.