Ubuntu for AMD 64 is the same as Ubuntu, only that it is optimized for use with a 64-bit processor, be it AMD or Intel. The upside in using Ubuntu 64 is that you will have increased performance when your ram is 4GB or greater because of the optimized architecture of 64bit. Any lower, you will not notice a difference between the two. The downside if it is that most softwares are made for 32bit, so your favorite app might not run on 64. If you are a newbie, I suggest you get the 32bit Ubuntu instead.
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Ubuntu for AMD 64 is the same as Ubuntu, only that it is optimized for use with a 64-bit processor, be it AMD or Intel. The upside in using Ubuntu 64 is that you will have increased performance when your ram is 4GB or greater because of the optimized architecture of 64bit. Any lower, you will not notice a difference between the two. The downside if it is that most softwares are made for 32bit, so your favorite app might not run on 64. If you are a newbie, I suggest you get the 32bit Ubuntu instead.