Somehow, the image I get from what you're describing is that of a bag of grain with a small hole gnawed in the corner: the more time passes, the smaller the bag becomes.

RAM, however, doesn't work that way (which is just as well or we'd have stray bits all over the floor around our computers!)

A "memory leak" is something that happens in an individual program or, on very rare occasions, within the operating system itself, and it produces a program that over time has an increasingly large appetite for memory. Typically memory leaks are because of sloppy programming, where, for example, a routine might request and instantiate a block of memory for an array each time it's called, but never free it up.

In the Unix world we'd be talking about malloc and free, the two key routines for managing memory in an application. On a Windows system there are equivalent system calls within just about all robust programming language environments.

However, since I believe we're not talking about memory leaks (and one more characteristic of a memory leak: the amount of free memory shrinks over time which you aren't seeing), I will instead suggest that what you're seeing is either:

1. Bad Memory - when your computer boots up, at one point it should indicate to you how much usable memory there is. Does it agree with what you've installed? You can also look in your BIOS configuration to find out.

(I have an older PC where I added 512MB of RAM to bring it up to 756MB, just to find out that the motherboard/BIOS doesn't support more than 512MB. But it indicated that to me during bootup.)

2. A Greedy OS - if your hardware does have all the memory available, you might well have some sort of spyware, virus or even legitimate application that's automatically started when your OS launches that's eating up tons of your memory.

One way you can check this is to use Microsoft's Task Manager, which can monitor memory usage among its many capabilities.

Hope this helps you out!

Another possibility for your system slowing down, by the way, is that you have a virus or some spyware. Even if that seems remote, you must have both a solid antivirus solution and anti-spyware solution. I recommend AVG Antivirus for the former and Spy Sweeper for the latter.