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RAM, SDRAM, DDR RAM? What is it all about? The novice might suddenly appear bemused or mystified at the brandishing of such 21st Century sorcery, but they are nothing more than acronyms which indicate memory in a computer.
So fear not, as we will finally put this confusion to rest in the following paragraphs to explain where the terms come from and what they mean.
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The acronym RAM simply stands for Random-Access Memory and is commonly known as the memory modules (or the modern DIMM’s) used in your computer in order to store information. The DIMM modules are inserted into slots in your motherboard (which commonly have up to four slots) and fixed via two clips at the side of each slot.
Hence it is data storage which enables your processor, via its control unit, to access and retrieve information, perhaps store it in its registers temporarily and use it to run a program. RAM is volatile and is cleared each time you switch your machine off, not permanent storage such as a hard drive (until formatted or otherwise anyway).
There are many types of RAM available, and when looking to upgrade your machine it isn’t enough to just mention RAM on its own. It is just a generic term for computer memory and is included with other prefixes (such as 'DDR SD' RAM or 'SDR SD' RAM) to specify exactly the type of module. Types of widely used RAM include Double or Single-Data Rate and others.
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The SD in SDRAM stands for synchronous-dynamic RAM and although developed in the 1970’s it gained popularity in the 1990’s to eventually replace older types of memory modules.
Synchronous essentially means that its operations are in-synch with your processor; it has a clock-input and it can be controlled by the system clock which also controls CPU operations. As such it is much faster since, in very simple terms, it is synchronized with both CPU and Front-side bus.
SDRAM is what is commonly used today from the Double-Data Rate (DDR) type 1 up to type 3 (DDR-3) all looking slightly different, i.e. the notch being in a different place, and offering different capabilities. DDR type 4 (DDR-4) is currently being developed, released in 2008, and is expected to be available by 2012.
Many motherboards now feature dual-channel memory which allows for the modules to be paired (i.e. slot 1-3, slot 2-4) and allows for improved memory usage and faster performance.
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That is essentially the difference between these terms. Now you can avoid confusion and be more specific about what you need, bearing in mind that just using RAM (a generic term for computer memory) isn't likely to get you anywhere when looking for upgrades.