Random-access memory (RAM) is a form of computer data storage. Purpose of the RAM is to temporarily store the necessary files (e.g., executable file and dynamic-link library files for a software you opened up) taken from the hard drive by the processor so that it can access them faster. This is because retrieving data from the hard drive takes longer than reading and writing on RAM. Bigger applications will require more space on the RAM and the more applications you run at the same time the more space will be needed. So, the more RAM you have the faster your computer will be, up to a point. Other factors, such as the processing power of your CPU, speed of your RAM, whether you have a 32-bit or 64-bit Windows, and other components of your system will limit the continuous increase in your computer's speed as you add more and more RAM. Unlike the hard drive, RAM does not store data permanently. Once you turn off the computer, the data in the RAM disappears.
You can read more about it here:
http://www.ddrmemoryupgrades.com/what_is_ram.html
http://searchmobilecomputing.techtarget.com/definition/RAM
http://computer.howstuffworks.com/question175.htm
http://en.wikipedia.org/wiki/Random-access_memory
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How much RAM do you need?
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Windows XP: At least 512MB, but 1GB or 2GB would be better.
Windows Vista/7: At least 2GB, but 4GB would be better.
If you are a serious gamer or do a lot of media editing, you'll need more RAM regardless of the OS. Note: that 32-bit operating system (OS) will only be able to utilize a maximum of 2-3GB. A 64-bit version will be able to utilize much more than that. So, if you plan on upgrading your memory to more than 3GB, you'll need to install a 64-bit Windows. To do that, you'll need to have a 64-bit processor (CPU). Read more about that here:
http://windows.microsoft.com/en-CA/windows-vista/32-bit-and-64-bit-Windows-frequently-asked-questions
http://support.microsoft.com/kb/827218
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How to buy the right RAM?
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You need to consider a number of factors:
▪ Memory for laptops (SODIMM) are different from those for desktops (DIMM).
▪ Capacity
▪ DDR2 or DDR3
▪ Speed: PC2-5300 (667MHz), PC2-6400(800MHz), etc.
▪ Latency timings
▪ Number of slots available on your computer
To make your life a lot easier, run the "Crucial Memory Scan". It'll tell you exactly what you need to purchase and how much memory you have. http://www.crucial.com/systemscanner/index.aspx They have a nice video on their site showing exactly how to run the scan. Watch the whole thing before you start.
If you have never installed RAM before, I would suggest that you purchase the right RAM and get someone (e.g., brother or a friend) who has done it before to install it for you, because you don't want to break anything inside.
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Where to buy?
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▪ Newegg: http://www.newegg.com/Store/Category.aspx?Category=17&name=Memory
▪ Amazon: http://www.amazon.com/PC-Components-Computer-Add-Ons-Computers/b/ref=amb_link_84661831_29?ie=UTF8&node=193870011&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-8&pf_rd_r=0S49S5VJHY3P1AMCYTP1&pf_rd_t=101&pf_rd_p=1261108362&pf_rd_i=172456
▪ NCIX: http://www.ncixus.com/products/index.php?mode=productdir