What can I do to improve the processing speed of my iMac?

Question

Hello Apple Community,
I have iMac - The 2.93 GHz processor, 4 Gigs of memory version and I'm having some processing problems. About six month ago my iMac started randomly doing the "Holy-Crap-I'm-going-to-start-processing-stuff-and-I'm-not-going-to-tell-you-wh at-it-is" sounds. You know, the excessive microclicking from the processing ongoings behind the screen. Well, six months ago, these events were pretty unpredictable, didn't last verylong, and had a rather large time interval between occurrances (like a week or two). However, this is now happening most every day and since I've never had this bad of an issue before, I was hoping someone on the forums could help.
I've run Disk Utility (probably more often than I should) and I've cleared out some HD space (under the assumption that when you have more disk space, you computer runs faster). But the problem persists. I am rather weary of any outside utility programs (Once I downloaded one from "recommended programs" pages on the apple website and it completely killed my MacBook's HD). I reallly have no idea where to go next... Should I empty out more disk space? Should I install more RAM? I bought this machine recently (within the last 2 years) and I really don't want to solution to my problem to be "you need to buy another computer." I fear the sounds that my comptuer is making are cries of pain from the CPU's dying breath and I would really appreciate any assistance in prolonging the livelihood of my poor iMac.
Cheers,
Chris

Answer 1

About OS X Memory Management and Usage
Reading system memory usage in Activity Monitor
Memory Management in Mac OS X
Performance Guidelines- Memory Management in Mac OS X
A detailed look at memory usage in OS X
Understanding top output in the Terminal
The amount of available RAM for applications is the sum of Free RAM and Inactive RAM. This will change as applications are opened and closed or change from active to inactive status. The Swap figure represents an estimate of the total amount of swap space required for VM if used, but does not necessarily indicate the actual size of the existing swap file. If you are really in need of more RAM that would be indicated by how frequently the system uses VM. If you open the Terminal and run the top command at the prompt you will find information reported on Pageins () and Pageouts (). Pageouts () is the important figure. If the value in the parentheses is 0 (zero) then OS X is not making instantaneous use of VM which means you have adequate physical RAM for the system with the applications you have loaded. If the figure in parentheses is running positive and your hard drive is constantly being used (thrashing) then you need more physical RAM.
Adding RAM only makes it possible to run more programs concurrently.  It doesn't speed up the computer nor make games run faster.  What it can do is prevent the system from having to use disk-based VM when it runs out of RAM because you are trying to run too many applications concurrently or using applications that are extremely RAM dependent.  It will improve the performance of applications that run mostly in RAM or when loading programs.
The above information is more meaningful than relying on what is provided by Activity Monitor. The amount of Free RAM is not some set number below which you need more RAM. Total available RAM is the sum of Free and Inactive RAM, so Free RAM by itself may be misleading. When you truly need more RAM is when the system starts relying on virtual memory from the HDD.
I don't mean to start an argument with Roger, but relying on Free RAM by itself is an oversimplification of the situation.