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The i586 is still a 32bit OS. The x86_64 is fully 64bits, though it is able to run 32bit software as well. The main advantages are (my opinion): 1. You have native address space far beyond the 4GB that you have with 32bit systems. Actually, you have (theoretically) access to 4GBx4GB = 16 petabytes of memory (real and virtual). On my x86_64 system, I have 8GB of memory (32GB max) which I plan on increasing soon to 16GB, and I use all of it between running other systems (XP) on virtual machines, risk analysis and modeling software for stock and options trading, video and audio processing, and so forth. 2. The processor in 64bit mode can handle integers of 64bits (long long int types) without fussing around with dual registers and inter-register arithmetic processing. This is a performance boost for software that does a lot of integer arithmetic, such as string searches, array processing, and supporting large file systems. 3. A virtual machine manager can support 64bit clients, so you can try out that Windows 7 or Vista OS in a virtual machine without sacrificing your system on the alter of Redmond. Why you would want to though is a topic for a discussion over a lot of beer or single-malt scotch... :-) 4. I used to think that an array of 4 billion of anything would handle any conceivable programming situation. Boy, was I wrong! That was probably true when I only had an 8 or 16 bit processor. But now, if I want to model REALLY large systems, like the weather, the human genome, particle physics, or stellar phenomena then a 64bit system is the only practical way. At my wife's lab they generate and reduce about a petabyte of raw data a day when the synchrotron is running. Trust me, they are using Scientific Linux (RHEL-derived) in 64bit mode. They went fully 64bit when the DEC Alpha chip first came out back in the early 90's. Big Science requires Big Chips! 5. I'm sure some things are faster on the 32bit systems, but I haven't run apples-to-apples comparison benchmarks. I do know that with a lot of memory you don't hit the swapper, so that makes stuff run faster on a loaded machine. I'm sure the fact that I have 8 cores (dual E5450 3GHz chips) has a lot to do with why I can do stuff on my system in 5-15 minutes that would take 2-5 hours on my old P4 3GHz Dell running 32bits. 6. More of everything is better, at least when it comes to processor power, RAM, disc space, and any kind of I/O. Heck, the new generation of video processors are faster (by about 100x) than our CPU's for numeric processing these days! They are running 128bits with 512bit memory channels. That's why you can build a personal multi-teraflop supercomputer using nothing but a few nVidia GPUs for raw processing power and a Pentium only for OS control and I/O management. Each GPU provides a teraflop of processing power. So for between $5K and $10K USD, you can build your own 3-4 teraflop supercomputer! Pant! Pant! I'm hungry already! [Modified by: Rubberman on January 21, 2009 07:03 PM]

Sometimes real fast is almost as good as real time. Remember, Google is your friend!

How much RAM can the system handle? In your case, this is the critical component. Also, remember that total RAM available is physical RAM + swap space, so you can exceed 4GB of memory in a system that has 4GB or less of physical memory. In this case, you will still need a 64bit OS.

Sometimes real fast is almost as good as real time. Remember, Google is your friend!

Like Rubberman said above, in your case total RAM exceeds 4GB, since you have 4GB Physical you should have at least 2GB swap, which is a total of 6GB. To see if your linux detects all of your physical memory, you can use a live ubuntu cd-rom from: http://www.ubuntu.com/getubuntu/download , at the buttom of the download page you will see "Custom options", just select 64bit version and hit download. Boot your computer using this cd-rom, then press Alt+F2 on the keyboard, type "xterm" then press enter, after that enter the command "free" and hit enter. This will show you how much memory you have, and how much is currently in use.

Rubberman, No I think that's definitely chipsets limit, intel's 945 chipset supports only 32-bit memory addressing. My computer is from HP and its BIOS is very limited in options, so there's nothing i can do about it.